U.S. patent application number 15/323046 was filed with the patent office on 2017-08-10 for metal oxide catalyzed radiofluorination.
This patent application is currently assigned to The Regents of the University of California. The applicant listed for this patent is The Regents of the University of California. Invention is credited to Mark Lazari, Federica Morgia, Maxim Sergeev, Robert Michael Van Dam.
Application Number | 20170224851 15/323046 |
Document ID | / |
Family ID | 55020022 |
Filed Date | 2017-08-10 |
United States Patent
Application |
20170224851 |
Kind Code |
A1 |
Sergeev; Maxim ; et
al. |
August 10, 2017 |
METAL OXIDE CATALYZED RADIOFLUORINATION
Abstract
Inter alia, the first titania-catalyzed
[.sup.18F]-radiofluorination in highly aqueous medium is provided.
In embodiments, the method utilizes titanium dioxide, 1:1
acetonitrile-thexyl alcohol solvent mixture and tetrabutylammonium
bicarbonate as a base. Radiolabeling may be directly performed with
aqueous [.sup.18F]fluoride without the need for drying/azeotroping
step, which reduces radiosynthesis time while keeping high fluoride
conversion. The general applicability of the synthetic strategy to
the synthesis of the wide range of PET probes from tosylated
precursors is demonstrated.
Inventors: |
Sergeev; Maxim; (Los
Angeles, CA) ; Morgia; Federica; (Los Angeles,
CA) ; Van Dam; Robert Michael; (Los Angeles, CA)
; Lazari; Mark; (North Hills, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Regents of the University of California |
Oakland |
CA |
US |
|
|
Assignee: |
The Regents of the University of
California
Oakland
CA
|
Family ID: |
55020022 |
Appl. No.: |
15/323046 |
Filed: |
July 2, 2015 |
PCT Filed: |
July 2, 2015 |
PCT NO: |
PCT/US2015/039095 |
371 Date: |
December 29, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62020840 |
Jul 3, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61K 51/04 20130101;
C07C 17/361 20130101; C07B 59/002 20130101; C07C 67/333 20130101;
C07D 207/09 20130101; A61K 51/0446 20130101; C07C 201/12 20130101;
C07D 207/16 20130101; C07C 17/361 20130101; A61K 51/0453 20130101;
C07D 213/61 20130101; C07C 67/307 20130101; C07D 217/22 20130101;
A61K 51/0459 20130101; C07D 215/18 20130101; A61K 51/0491 20130101;
C07B 59/005 20130101; C07C 17/361 20130101; C07C 253/30 20130101;
C07B 59/001 20130101; C07C 255/50 20130101; C07C 25/13 20130101;
C07C 19/08 20130101; C07C 205/12 20130101; C07C 23/10 20130101;
C07C 69/76 20130101; C07C 22/08 20130101; C07C 25/22 20130101; C07B
59/00 20130101; C07C 201/12 20130101; C07D 241/16 20130101; B01J
21/063 20130101; C07D 405/04 20130101; C07C 17/361 20130101; C07H
19/052 20130101; C07D 405/06 20130101; C07C 17/361 20130101; C07B
2200/05 20130101; C07C 253/30 20130101; C07C 17/361 20130101; C07C
67/307 20130101; C07C 2601/14 20170501; A61K 51/0455 20130101 |
International
Class: |
A61K 51/04 20060101
A61K051/04; C07B 59/00 20060101 C07B059/00; C07C 17/361 20060101
C07C017/361; C07H 19/052 20060101 C07H019/052; C07D 207/16 20060101
C07D207/16; B01J 21/06 20060101 B01J021/06; C07C 67/333 20060101
C07C067/333; C07C 201/12 20060101 C07C201/12; C07C 253/30 20060101
C07C253/30; C07D 217/22 20060101 C07D217/22; C07D 241/16 20060101
C07D241/16; C07D 213/61 20060101 C07D213/61; C07D 207/09 20060101
C07D207/09; C07D 405/06 20060101 C07D405/06 |
Claims
1. A method of forming an [.sup.18F]-labeled organic compound in an
aqueous medium, the method comprising: combining within an aqueous
medium an aqueous [.sup.18F] fluoride, a transition metal oxide and
an organic compound precursor comprising a reactive carbon; and
allowing said aqueous [.sup.18F] fluoride source to react with said
reactive carbon thereby forming said [.sup.18F]-labeled organic
compound.
2. The method of claim 1, wherein said organic compound precursor
is an aryl organic compound precursor and said [.sup.18F]-labeled
organic compound is an [.sup.18F]-labeled aryl organic
compound.
3. The method of claim 1, wherein said aqueous medium is less than
about 5%, 10%, 15%, 20% or 25% water.
4. The method of claim 1, wherein said [.sup.18F]-labeled organic
compound is a positron emission tomography probe.
5. The method of claim 1, wherein said reacting is SN2 nucleophilic
substitution reacting.
6. The method of claim 1, wherein the reactive carbon forms part of
a substituted or unsubstituted aryl, substituted or unsubstituted
heteroaryl, substituted or unsubstituted alkyl, substituted or
unsubstituted heteroalkyl, substituted or unsubstituted cycloalkyl
or substituted or unsubstituted heterocycloalkyl.
7. The method of claim 1, wherein the reactive carbon forms part of
a substituted or unsubstituted alkyl, substituted or unsubstituted
heteroalkyl, substituted or unsubstituted cycloalkyl or substituted
or unsubstituted heterocycloalkyl.
8. The method of claim 1, wherein said transition metal oxide is
chromium(VI) oxide, molybdenum(VI) oxide, platinum(IV) oxide,
rhenium(VI) oxide, rhenium(VII) oxide, ruthenium(IV) oxide,
tantalum(V) oxide, tin(IV) oxide, vanadium(IV) oxide, vanadium(V)
oxide, yttrium(III) oxide, zirconium(IV) oxide, chromium(III)
oxide, bismuth(III) oxide, manganese(IV) oxide, tungsten(IV) oxide,
molybdenum(IV) oxide, tungsten(VI) oxide, palladium(II) oxide,
iron(II) oxide, zinc(II) oxide, indium(III) oxide, copper(II)
oxide, niobium(IV) oxide, niobium(V) oxide, or titanium(IV)
oxide.
9. The method of claim 1, wherein said transition metal oxide is
palladium(II) oxide, iron(II) oxide, zinc(II) oxide, indium(III)
oxide, copper(II) oxide, niobium(IV) oxide, niobium(V) oxide, or
titanium(IV) oxide.
10. The method of claim 1, wherein said transition metal oxide is
TiO.sub.2, NbO.sub.2, Nb.sub.2O.sub.5, In.sub.2O.sub.3, or CuO.
11. The method of claim 1, wherein said aqueous medium further
comprises a base.
12. The method of claim 1, wherein said aqueous medium further
comprises an ammonium base.
13. The method of claim 1, wherein said aqueous medium further
comprises an ammonium bicarbonate base.
14. The method of claim 1, wherein said aqueous medium further
comprises an alcohol co-solvent, optionally MeOH, EtOH, n-PrOH,
i-PrOH, t-BuOH, tHexOH, n-octanol or cyclohexanol.
15. The method of claim 1, wherein said aqueous medium further
comprises an alcohol co-solvent, optionally t-BuOH, tHexOH,
n-octanol or cyclohexanol.
16. The method of claim 1, wherein said reactive compound or said
organic compound precursor is attached to a tosylate,
benzenesulfonyl, 4-nitrobenzenesulfonyl, methanesulfonyl,
ethanesulfonyl, trifluoromethylsulfonyl, or
1,1,2,2,2-pentafluoroethane-1-sulfonyl moiety.
17. The method of claim 1, wherein said aqueous [.sup.18F] fluoride
is generated from a cyclotron and is not dried or azeotroped after
generation from said cyclotron.
Description
BACKGROUND OF THE INVENTION
[0001] Positron emission tomography (PET) is an extremely effective
imaging tool in preclinical and clinical cancer research to
visualize physiological state or changes in the living body, to
investigate the mechanism of disease, and to quantify biological
processes such as receptor occupancy, cell proliferation, metabolic
activity, apoptosis, and gene expression. Since PET allows
measurement of phenotypic changes associated with a malignant
condition with high sensitivity, the onset of a particular disease
such as cancer can be detected, diagnosed, and treated at an early
stage prior to the development of metastasis. Typically,
.sup.18F-labeled PET tracers are synthesized using nucleophilic
fluorination of activated precursors with
[.sup.18O]H.sub.2O/[.sup.18F]fluoride obtained from cyclotron. Due
to high F-ion solvation energy, aqueous fluoride is inactive unless
it is released from its aqueous surrounding. This is usually
achieved by mixing aqueous fluoride with base (KHCO.sub.3,
K.sub.2CO.sub.3 etc.) and phase transfer agent (e.g.,
Kryptofix-222) and azeotropic drying of the resulting solution with
acetonitrile. The dried active complex (e.g.,
[.sup.18F]KF/K.sub.222) is further used for radiolabelling.
Depending on technical method of fluoride activation (i.e.
micro-chip or macro-reactor evaporation, cartridge solvent
exchange), this procedure takes 20-30 minutes and some loss of
initial radioactivity is observed..sup.[4,5]
[0002] To reduce the need for a lengthy drying process, there has
been interest during the last years in the development of
radiofluorination methods that allow to use aqueous
[.sup.18F]fluoride directly without the traditional
drying/azeotroping step. Several novel approaches were suggested,
such as enzymatic and transition-metal catalysis, development of
specific substrates and fluorinating reagents. The majority of
methods which are directly using the cyclotron-delivered
[.sup.18O]H.sub.2O/[.sup.18F]fluoride leads to low-to-moderate
fluoride conversion and yields of fluorinated product, while
reactions are conducted in aqueous-organic medium with water
content up to 20% and mostly these methods deal with aromatic
nucleophilic fluorination. Titania is widely used in a variety of
chemical processes, including electro- and photochemistry. Along
with broad catalytic activity it possesses strong ability to adsorb
water from the surrounding medium.
[0003] Provided herein, inter alia, is a conceptually new method
based on titania as a catalyst. Embodiments include highly
efficient and fast route for radiofluorination is suitable for
aromatic, aliphatic and cycloaliphatic precursors in
organic-aqueous medium with maximum tolerated water content up to
25%.
BRIEF SUMMARY OF THE INVENTION
[0004] Provided herein, inter alia, is a catalytic approach to
carry out the synthesis in reaction medium with much higher water
content (up to 25% water in the reaction mixture) than is normally
possible with these precursors.
[0005] Typically, the source of fluorine-18 is a cyclotron
(yielding [F-18]fluoride in [O-18]water). Therefore, the ability to
perform reactions with high water content eliminates the need for
the time-consuming preliminary steps of evaporative drying and
azeotropic distillation (with MeCN) that is typically needed to
remove water prior to the radiolabeling reaction.
[0006] Provided herein, inter alia, are basic, transition and
rare-earth metal oxides as a catalyst for nucleophilic SN2-type
radiofluorination reaction of organic substrates containing an
active leaving group. Examples of leaving groups are
benzenesulfonyl, 4-methylbenzenesulfonyl (tosylate),
4-nitrobenzenesulfonyl (nosylate), methanesulfonyl (mesylate),
ethanesulfonyl, trifluoromethylsulfonyl (triflate), or
1,1,2,2,2-pentafluoroethane-1-sulfonyl.
[0007] The resulting radiolabeled molecules are useful, for
example, as tracers for positron emission tomography (PET) in
either research or clinical studies. The approach may also be
useful in the field of fluorine chemistry to facilitate the
production of fluorine-containing molecules such as
pharmaceuticals.
[0008] Materials used include commercially available metal oxide
catalysts (Sigma-Aldrich), .sup.18F-fluoride (produced in UCLA
Biomedical cyclotron),a few standard PET tracer precursors (ABX
GmbH), commercially available solvents and reagents
(Sigma-Aldrich).
[0009] Solutions containing a metal oxide catalyst and a precursor
may be pre-incubated. Aqueous [F-18]fluoride containing a phase
transfer agent may then be added. Finally, the mixture may be
heated thereby performing the reaction.
[0010] Exemplary procedure (titanium dioxide catalyzed synthesis of
[.sup.18F]fallypride): Prior to use titanium dioxide was calcined
at 550.degree. C. during 12 h. A screw-cap scintillation vial was
filled with TiO.sub.2 (11.5 mg, 0.14 mmol) and tosyl-fallypride
(2.3 .mu.mol) solution in 1:1 mixture of acetonitrile and thexyl
alcohol (30 .mu.L). Vial was capped and incubated at room
temperature for 1 hour. The aqueous solution of
[.sup.18F]F.sup.-/TBAHCO.sub.3 (1.5-3 mCi, 10 .mu.l) was then added
into pre-incubated vial, resulting into 25% water content in
reaction mixture. The vial was capped and transferred to a Peltier
heater. Reaction was performed at 130.degree. C. for 5 minutes. The
product was then extracted with methanol (2.times.200 .mu.l).
Combined extracts were thoroughly filtered through a Whatman
`Anotop 10 Plus` filter (0.02 .mu.m) and the radiolabeled product
content was analyzed by radio-TLC and HPLC.
[0011] For TiO.sub.2 catalyst and the fallypride precursor, the
reaction conditions may be 130.degree. C. and 5 min reaction time
with 25% water content, but the reaction can also be performed at
temperature range of about 90.degree. C. to about 140.degree. C.,
time range of about 3 to about 10 minutes, water content range of
about 5 to about 25%. Ranges might be extended with additional
optimization, or with other precursors or other metal oxide
catalysts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a graph showing the evaluation of water content in
TiO.sub.2-catalyzed radiofluorination of tosyl-fallypride.
[0013] FIG. 2 is a graph showing the effect of water content on RCC
in TiO.sub.2-catalyzed radiofluorination of tosyl-fallypride.
[0014] FIG. 3 is a series of graphs showing (left) radioactivity
extraction and trapping at different catalyst loading amount.
Triangles for radioactivity counted in organic extract, squares for
radioactivity trapped in catalytic layer; (right) radiochemical
purity of 2a.
[0015] FIG. 4 is a graph showing the effects of catalyst loading
amount on RCC.
[0016] FIG. 5 is a graph showing the evaluation of catalyst loading
amount.
[0017] FIG. 6 is a graph showing the radioactivity extraction
curves at different catalyst loading amount. Black triangles for
organic extract, gray rhombi for trapping in catalytic layer.
[0018] FIG. 7 is a graph showing the evaluation of temperature
profile in TiO.sub.2-catalyzed radiofluorination of
tosyl-fallypride.
[0019] FIG. 8 is a graph showing the effect of temperature on RCC
in TiO.sub.2-catalyzed radiofluorination of tosyl-fallypride.
[0020] FIG. 9 is a graph showing the evaluation of time profile in
TiO.sub.2-catalyzed radiofluorination of tosyl-fallypride at
130.degree. C.
[0021] FIG. 10 is a graph showing the effect of reaction time on
RCC of TiO.sub.2-catalyzed radiofluorination of tosyl-fallypride
la. Reaction was performed at 130.degree. C.
[0022] FIG. 11 is a graph showing the evaluation of
substrate-catalyst incubation time.
[0023] FIG. 12 is a graph showing the effect of substrate-catalyst
incubation time on RCC.
[0024] FIG. 13 is a graph showing the effect of DMSO addition on
radiofluorination of 1a. A) Radioactivity extraction efficiency; B)
Radiochemical conversion.
[0025] FIG. 14 is a graph showing the evaluation of
radiofluorination time profile after substrate-catalyst
incubation.
[0026] FIG. 15 is a graph showing the evaluation of
radiofluorination time profile after 1 hr substrate-catalyst
incubation.
[0027] FIG. 16 is a series of graphs showing a) Exemplary
HPLC-chromatogram of micro-chip [.sup.18F]Fallypride preparation
(crude product, prior to final purification): Inset shows enlarged
UV-area of target compound 2a. Top is UV absorbance signal, bottom
is gamma signal. b) Co-injection with cold standard,
[.sup.19F]Fallypride.
[0028] FIG. 17 is a series of graphs showing a) Exemplary
HPLC-chromatogram of non-optimized TiO.sub.2-catalyzed
[.sup.18F]Fallypride preparation (crude product, after extraction
and before final purification). Top is UV absorbance signal; bottom
is gamma signal. b) Co-injection with cold standard,
[.sup.19F]Fallypride.
[0029] FIG. 18 is a series of graphs showing HPLC-chromatogram of
injectable [.sup.18F]Fallypride formulation.
[0030] FIG. 19 is a series of graphs showing Determination of
optimal catalyst amount for radiolabeling of 1a, 1i, 1q and 1t.
[0031] FIG. 20 is a picture showing a proposed mechanism for
TiO.sub.2-catalyzed radiofluorination. SN.sub.2 substitution is
improved with alcohol as a co-solvent, perhaps by inclusion in
intermediate complex formation as determined by Oh et al.
[0032] FIG. 21 is a graph showing the correlation between reaction
time and fluorination efficiency in scaled-up catalytic
radiolabeling of 1a. Values are averaged from n=9 experiments for 5
min runs, and n=6 for each of 8 and 15 min experiments.
[0033] FIG. 22 is a picture showing additional substrates with
sulfonyl-containing leaving groups and their corresponding
hydrolysates.
[0034] FIG. 23 is a graph showing Transition metal oxides screening
of the Temperature profile.
[0035] FIG. 24 is a graph showing Transition metal oxides screening
of the Time profile.
DETAILED DESCRIPTION OF THE INVENTION
[0036] The abbreviations used herein have their conventional
meaning within the chemical and biological arts. The chemical
structures and formulae set forth herein are constructed according
to the standard rules of chemical valency known in the chemical
arts.
[0037] Where substituent groups are specified by their conventional
chemical formulae, written from left to right, they equally
encompass the chemically identical substituents that would result
from writing the structure from right to left, e.g., --CH2O-- is
equivalent to --OCH2-.
[0038] The term "alkyl," by itself or as part of another
substituent, means, unless otherwise stated, a straight (i.e.,
unbranched) or branched carbon chain (or carbon), or combination
thereof, which may be fully saturated, mono- or polyunsaturated and
can include mono-, di- and multivalent radicals, having the number
of carbon atoms designated (i.e., C.sub.1-C.sub.10 means one to ten
carbons). Alkyl is an uncyclized chain. Examples of saturated
hydrocarbon radicals include, but are not limited to, groups such
as methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, isobutyl,
sec-butyl, (cyclohexyl)methyl, homologs and isomers of, for
example, n-pentyl, n-hexyl, n-heptyl, n-octyl, and the like. An
unsaturated alkyl group is one having one or more double bonds or
triple bonds. Examples of unsaturated alkyl groups include, but are
not limited to, vinyl, 2-propenyl, crotyl, 2-isopentenyl,
2-(butadienyl), 2,4-pentadienyl, 3-(1,4-pentadienyl), ethynyl, 1-
and 3-propynyl, 3-butynyl, and the higher homologs and isomers. An
alkoxy is an alkyl attached to the remainder of the molecule via an
oxygen linker (--O--).
[0039] The term "alkylene," by itself or as part of another
substituent, means, unless otherwise stated, a divalent radical
derived from an alkyl, as exemplified, but not limited by,
--CH.sub.2CH.sub.2CH.sub.2CH.sub.2--. Typically, an alkyl (or
alkylene) group will have from 1 to 24 carbon atoms, with those
groups having 10 or fewer carbon atoms being preferred in the
present invention. A "lower alkyl" or "lower alkylene" is a shorter
chain alkyl or alkylene group, generally having eight or fewer
carbon atoms. The term "alkenylene," by itself or as part of
another substituent, means, unless otherwise stated, a divalent
radical derived from an alkene.
[0040] The term "heteroalkyl," by itself or in combination with
another term, means, unless otherwise stated, a stable straight or
branched chain, or combinations thereof, including at least one
carbon atom and at least one heteroatom selected from the group
consisting of O, N, P, Si, and S, and wherein the nitrogen and
sulfur atoms may optionally be oxidized, and the nitrogen
heteroatom may optionally be quaternized. The heteroatom(s) O, N,
P, S, B, As, and Si may be placed at any interior position of the
heteroalkyl group or at the position at which the alkyl group is
attached to the remainder of the molecule. Heteroalkyl is an
uncyclized chain. Examples include, but are not limited to:
--CH.sub.2--CH.sub.2--O--CH.sub.3,
--CH.sub.2--CH.sub.2--NH--CH.sub.3,
--CH.sub.2--CH.sub.2--N(CH.sub.3)--CH.sub.3,
--CH.sub.2--S--CH.sub.2--CH.sub.3, --CH.sub.2--CH.sub.2,
--S(O)--CH.sub.3, --CH.sub.2--CH.sub.2--S(O).sub.2--CH.sub.3,
--CH--CH--O--CH.sub.3, --Si(CH.sub.3).sub.3,
--CH.sub.2--CH.dbd.N--OCH.sub.3,
--CH.dbd.CH--N(CH.sub.3)--CH.sub.3, --O--CH.sub.3,
--O--CH.sub.2--CH.sub.3, and --CN. Up to two or three heteroatoms
may be consecutive, such as, for example, --CH.sub.2--NH--OCH.sub.3
and --CH.sub.2--O--Si(CH.sub.3).sub.3.
[0041] Similarly, the term "heteroalkylene," by itself or as part
of another substituent, means, unless otherwise stated, a divalent
radical derived from heteroalkyl, as exemplified, but not limited
by, --CH.sub.2--CH.sub.2--S--CH.sub.2--CH.sub.2-- and
--CH.sub.2--S--CH.sub.2--CH.sub.2--NH--CH.sub.2--. For
heteroalkylene groups, heteroatoms can also occupy either or both
of the chain termini (e.g., alkyleneoxy, alkylenedioxy,
alkyleneamino, alkylenediamino, and the like). Still further, for
alkylene and heteroalkylene linking groups, no orientation of the
linking group is implied by the direction in which the formula of
the linking group is written. For example, the formula
--C(O).sub.2R'-- represents both --C(O).sub.2R'-- and
--R'C(O).sub.2--. As described above, heteroalkyl groups, as used
herein, include those groups that are attached to the remainder of
the molecule through a heteroatom, such as --C(O)R', --C(O)NR',
--NR'R'', --OR', --SR', and/or --SO.sub.2R'. Where "heteroalkyl" is
recited, followed by recitations of specific heteroalkyl groups,
such as --NR'R'' or the like, it will be understood that the terms
heteroalkyl and --NR'R'' are not redundant or mutually exclusive.
Rather, the specific heteroalkyl groups are recited to add clarity.
Thus, the term "heteroalkyl" should not be interpreted herein as
excluding specific heteroalkyl groups, such as --NR'R'' or the
like.
[0042] The terms "cycloalkyl" and "heterocycloalkyl," by themselves
or in combination with other terms, mean, unless otherwise stated,
cyclic versions of "alkyl" and "heteroalkyl," respectively.
Cycloalkyl and heteroalkyl are not aromatic. Additionally, for
heterocycloalkyl, a heteroatom can occupy the position at which the
heterocycle is attached to the remainder of the molecule. Examples
of cycloalkyl include, but are not limited to, cyclopropyl,
cyclobutyl, cyclopentyl, cyclohexyl, 1-cyclohexenyl,
3-cyclohexenyl, cycloheptyl, and the like. Examples of
heterocycloalkyl include, but are not limited to,
1-(1,2,5,6-tetrahydropyridyl), 1-piperidinyl, 2-piperidinyl,
3-piperidinyl, 4-morpholinyl, 3-morpholinyl, tetrahydrofuran-2-yl,
tetrahydrofuran-3-yl, tetrahydrothien-2-yl, tetrahydrothien-3-yl,
1-piperazinyl, 2-piperazinyl, and the like. A "cycloalkylene" and a
"heterocycloalkylene," alone or as part of another substituent,
means a divalent radical derived from a cycloalkyl and
heterocycloalkyl, respectively.
[0043] The terms "halo" or "halogen," by themselves or as part of
another substituent, mean, unless otherwise stated, a fluorine,
chlorine, bromine, or iodine atom. Additionally, terms such as
"haloalkyl" are meant to include monohaloalkyl and polyhaloalkyl.
For example, the term "halo(C.sub.1-C.sub.4)alkyl" includes, but is
not limited to, fluoromethyl, difluoromethyl, trifluoromethyl,
2,2,2-trifluoroethyl, 4-chlorobutyl, 3-bromopropyl, and the
like.
[0044] The term "acyl" means, unless otherwise stated, --C(O)R
where R is a substituted or unsubstituted alkyl, substituted or
unsubstituted cycloalkyl, substituted or unsubstituted heteroalkyl,
substituted or unsubstituted heterocycloalkyl, substituted or
unsubstituted aryl, or substituted or unsubstituted heteroaryl.
[0045] The term "aryl" means, unless otherwise stated, a
polyunsaturated, aromatic, hydrocarbon substituent, which can be a
single ring or multiple rings (preferably from 1 to 3 rings) that
are fused together (i.e., a fused ring aryl) or linked covalently.
A fused ring aryl refers to multiple rings fused together wherein
at least one of the fused rings is an aryl ring. The term
"heteroaryl" refers to aryl groups (or rings) that contain at least
one heteroatom such as N, O, or S, wherein the nitrogen and sulfur
atoms are optionally oxidized, and the nitrogen atom(s) are
optionally quaternized. Thus, the term "heteroaryl" includes fused
ring heteroaryl groups (i.e., multiple rings fused together wherein
at least one of the fused rings is a heteroaromatic ring). A
5,6-fused ring heteroarylene refers to two rings fused together,
wherein one ring has 5 members and the other ring has 6 members,
and wherein at least one ring is a heteroaryl ring. Likewise, a
6,6-fused ring heteroarylene refers to two rings fused together,
wherein one ring has 6 members and the other ring has 6 members,
and wherein at least one ring is a heteroaryl ring. And a 6,5-fused
ring heteroarylene refers to two rings fused together, wherein one
ring has 6 members and the other ring has 5 members, and wherein at
least one ring is a heteroaryl ring. A heteroaryl group can be
attached to the remainder of the molecule through a carbon or
heteroatom. Non-limiting examples of aryl and heteroaryl groups
include phenyl, 1-naphthyl, 2-naphthyl, 4-biphenyl, 1-pyrrolyl,
2-pyrrolyl, 3-pyrrolyl, 3-pyrazolyl, 2-imidazolyl, 4-imidazolyl,
pyrazinyl, 2-oxazolyl, 4-oxazolyl, 2-phenyl-4-oxazolyl, 5-oxazolyl,
3-isoxazolyl, 4-isoxazolyl, 5-isoxazolyl, 2-thiazolyl, 4-thiazolyl,
5-thiazolyl, 2-furyl, 3-furyl, 2-thienyl, 3-thienyl, 2-pyridyl,
3-pyridyl, 4-pyridyl, 2-pyrimidyl, 4-pyrimidyl, 5-benzothiazolyl,
purinyl, 2-benzimidazolyl, 5-indolyl, 1-isoquinolyl, 5-isoquinolyl,
2-quinoxalinyl, 5-quinoxalinyl, 3-quinolyl, and 6-quinolyl.
Substituents for each of the above noted aryl and heteroaryl ring
systems are selected from the group of acceptable substituents
described below. An "arylene" and a "heteroarylene," alone or as
part of another substituent, mean a divalent radical derived from
an aryl and heteroaryl, respectively. A heteroaryl group
substituent may be a --O-- bonded to a ring heteroatom
nitrogen.
[0046] A "fused ring aryl-heterocycloalkyl" is an aryl fused to a
heterocycloalkyl. A "fused ring heteroaryl-heterocycloalkyl" is a
heteroaryl fused to a heterocycloalkyl. A "fused ring
heterocycloalkyl-cycloalkyl" is a heterocycloalkyl fused to a
cycloalkyl. A "fused ring heterocycloalkyl-heterocycloalkyl" is a
heterocycloalkyl fused to another heterocycloalkyl. Fused ring
aryl-heterocycloalkyl, fused ring heteroaryl-heterocycloalkyl,
fused ring heterocycloalkyl-cycloalkyl, or fused ring
heterocycloalkyl-heterocycloalkyl may each independently be
unsubstituted or substituted with one or more of the substituents
described herein. Fused ring aryl-heterocycloalkyl, fused ring
heteroaryl-heterocycloalkyl, fused ring
heterocycloalkyl-cycloalkyl, or fused ring
heterocycloalkyl-heterocycloalkyl may each independently be named
according to the size of each of the fused rings. Thus, for
example, 6,5 aryl-heterocycloalkyl fused ring describes a 6
membered aryl moiety fused to a 5 membered heterocycloalkyl.
Spirocyclic rings are two or more rings wherein adjacent rings are
attached through a single atom. The individual rings within
spirocyclic rings may be identical or different. Individual rings
in spirocyclic rings may be substituted or unsubstituted and may
have different substituents from other individual rings within a
set of spirocyclic rings. Possible substituents for individual
rings within spirocyclic rings are the possible substituents for
the same ring when not part of spirocyclic rings (e.g. substituents
for cycloalkyl or heterocycloalkyl rings). Spirocylic rings may be
substituted or unsubstituted cycloalkyl, substituted or
unsubstituted cycloalkylene, substituted or unsubstituted
heterocycloalkyl or substituted or unsubstituted
heterocycloalkylene and individual rings within a spirocyclic ring
group may be any of the immediately previous list, including having
all rings of one type (e.g. all rings being substituted
heterocycloalkylene wherein each ring may be the same or different
substituted heterocycloalkylene). When referring to a spirocyclic
ring system, heterocyclic spirocyclic rings means a spirocyclic
rings wherein at least one ring is a heterocyclic ring and wherein
each ring may be a different ring. When referring to a spirocyclic
ring system, substituted spirocyclic rings means that at least one
ring is substituted and each substituent may optionally be
different.
[0047] The term "oxo," as used herein, means an oxygen that is
double bonded to a carbon atom.
[0048] The term "thio," as used herein, means a sulfur that is
single bonded to carbon or to another sulfur.
[0049] Each of the above terms (e.g., "alkyl," "heteroalkyl,"
"aryl," and "heteroaryl") includes both substituted and
unsubstituted forms of the indicated radical. Preferred
substituents for each type of radical are provided below.
[0050] Substituents for the alkyl and heteroalkyl radicals
(including those groups often referred to as alkylene, alkenyl,
heteroalkylene, heteroalkenyl, alkynyl, cycloalkyl,
heterocycloalkyl, cycloalkenyl, and heterocycloalkenyl) can be one
or more of a variety of groups selected from, but not limited to,
--OR', .dbd.O, .dbd.NR', .dbd.N--OR', --NR'R'', --SR', -halogen,
--SiR'R''R''', --OC(O)R', --C(O)R', --CO.sub.2R', --CONR'R'',
--OC(O)NR'R'', --NR''C(O)R', --NR'--C(O)NR''R''',
--NR''C(O).sub.2R', --NR--C(NR'R''R''').dbd.NR'''',
--NR--C(NR'R'').dbd.NR''', --S(O)R', --S(O).sub.2R',
--S(O).sub.2NR'R'', --NRSO.sub.2R', --NR'NR''R''', --ONR'R'',
--NR'C.dbd.(O)NR''NR'''R'''', --CN, --NO.sub.2, --NR'SO.sub.2R'',
--NR'C.dbd.(O)R'', --NR'C(O)--OR'', --NR'OR'', in a number ranging
from zero to (2m'+1), where m' is the total number of carbon atoms
in such radical. R, R', R'', R''', and R'''' each preferably
independently refer to hydrogen, substituted or unsubstituted
heteroalkyl, substituted or unsubstituted cycloalkyl, substituted
or unsubstituted heterocycloalkyl, substituted or unsubstituted
aryl (e.g., aryl substituted with 1-3 halogens), substituted or
unsubstituted heteroaryl, substituted or unsubstituted alkyl,
alkoxy, or thioalkoxy groups, or arylalkyl groups. When a compound
of the invention includes more than one R group, for example, each
of the R groups is independently selected as are each R', R'',
R''', and R'''' group when more than one of these groups is
present. When R' and R'' are attached to the same nitrogen atom,
they can be combined with the nitrogen atom to form a 4-, 5-, 6-,
or 7-membered ring. For example, --NR'R'' includes, but is not
limited to, 1-pyrrolidinyl and 4-morpholinyl. From the above
discussion of substituents, one of skill in the art will understand
that the term "alkyl" is meant to include groups including carbon
atoms bound to groups other than hydrogen groups, such as haloalkyl
(e.g., --CF.sub.3 and --CH.sub.2CF.sub.3) and acyl (e.g.,
--C(O)CH.sub.3, --C(O)CF.sub.3, --C(O)CH.sub.2OCH.sub.3, and the
like).
[0051] Similar to the substituents described for the alkyl radical,
substituents for the aryl and heteroaryl groups are varied and are
selected from, for example: --OR', --NR'R'', --SR', -halogen,
--SiR'R''R''', --OC(O)R', --C(O)R', --CO.sub.2R', --CONR'R'',
--OC(O)NR'R'', --NR''C(O)R', --NR'--C(O)NR''R''',
--NR''C(O).sub.2R', --NR--C(NR'R''R''').dbd.NR'''',
--NR--C(NR'R'').dbd.NR''', --S(O)R', --S(O).sub.2R',
--S(O).sub.2NR'R'', --NRSO.sub.2R', --NR'NR''R''', --ONR'R'',
--NR'C.dbd.(O)NR''NR'''R'''', --CN, --NO.sub.2, --R', --N.sub.3,
--CH(Ph).sub.2, fluoro(C.sub.1-C.sub.4)alkoxy, and
fluoro(C.sub.1-C.sub.4)alkyl, --NR'SO.sub.2R'', --NR'C.dbd.(O)R'',
--NR'C(O)--OR'', --NR'OR'', in a number ranging from zero to the
total number of open valences on the aromatic ring system; and
where R', R'', R''', and R'''' are preferably independently
selected from hydrogen, substituted or unsubstituted alkyl,
substituted or unsubstituted heteroalkyl, substituted or
unsubstituted cycloalkyl, substituted or unsubstituted
heterocycloalkyl, substituted or unsubstituted aryl, and
substituted or unsubstituted heteroaryl. When a compound of the
invention includes more than one R group, for example, each of the
R groups is independently selected as are each R', R'', R''', and
R'''' groups when more than one of these groups is present.
[0052] Substituents for rings (e.g. cycloalkyl, heterocycloalkyl,
aryl, heteroaryl, cycloalkylene, heterocycloalkylene, arylene, or
heteroarylene) may be depicted as substituents on the ring rather
than on a specific atom of a ring (commonly referred to as a
floating substituent). In such a case, the substituent may be
attached to any of the ring atoms (obeying the rules of chemical
valency) and in the case of fused rings or spirocyclic rings, a
substituent depicted as associated with one member of the fused
rings or spirocyclic rings (a floating substituent on a single
ring), may be a substituent on any of the fused rings or
spirocyclic rings (a floating substituent on multiple rings). When
a substituent is attached to a ring, but not a specific atom (a
floating substituent), and a subscript for the substituent is an
integer greater than one, the multiple substituents may be on the
same atom, same ring, different atoms, different fused rings,
different spirocyclic rings, and each substituent may optionally be
different. Where a point of attachment of a ring to the remainder
of a molecule is not limited to a single atom (a floating
substituent), the attachment point may be any atom of the ring and
in the case of a fused ring or spirocyclic ring, any atom of any of
the fused rings or spirocyclic rings while obeying the rules of
chemical valency. Where a ring, fused rings, or spirocyclic rings
contain one or more ring heteroatoms and the ring, fused rings, or
spirocyclic rings are shown with one more floating substituents
(including, but not limited to, points of attachment to the
remainder of the molecule), the floating substituents may be bonded
to the heteroatoms. Where the ring heteroatoms are shown bound to
one or more hydrogens (e.g. a ring nitrogen with two bonds to ring
atoms and a third bond to a hydrogen) in the structure or formula
with the floating substituent, when the heteroatom is bonded to the
floating substituent, the substituent will be understood to replace
the hydrogen, while obeying the rules of chemical valency.
[0053] Two or more substituents may optionally be joined to form
aryl, heteroaryl, cycloalkyl, or heterocycloalkyl groups. Such
so-called ring-forming substituents are typically, though not
necessarily, found attached to a cyclic base structure. In one
embodiment, the ring-forming substituents are attached to adjacent
members of the base structure. For example, two ring-forming
substituents attached to adjacent members of a cyclic base
structure create a fused ring structure. In another embodiment, the
ring-forming substituents are attached to a single member of the
base structure. For example, two ring-forming substituents attached
to a single member of a cyclic base structure create a spirocyclic
structure. In yet another embodiment, the ring-forming substituents
are attached to non-adjacent members of the base structure.
[0054] Two of the substituents on adjacent atoms of the aryl or
heteroaryl ring may optionally form a ring of the formula
-T-C(O)--(CRR').sub.q--U--, wherein T and U are independently
--NR--, --O--, --CRR'--, or a single bond, and q is an integer of
from 0 to 3. Alternatively, two of the substituents on adjacent
atoms of the aryl or heteroaryl ring may optionally be replaced
with a substituent of the formula -A-(CH.sub.2).sub.r--B--, wherein
A and B are independently --CRR'--, --O--, --NR--, --S--, --S(O)--,
--S(O).sub.2--, --S(O).sub.2NR'--, or a single bond, and r is an
integer of from 1 to 4. One of the single bonds of the new ring so
formed may optionally be replaced with a double bond.
Alternatively, two of the substituents on adjacent atoms of the
aryl or heteroaryl ring may optionally be replaced with a
substituent of the formula
--(CRR').sub.s--X'--(C''R''R''').sub.d--, where s and d are
independently integers of from 0 to 3, and X' is --O--, --NR'--,
--S--, --S(O)--, --S(O).sub.2--, or --S(O).sub.2NR'--. The
substituents R, R', R'', and R''' are preferably independently
selected from hydrogen, substituted or unsubstituted alkyl,
substituted or unsubstituted heteroalkyl, substituted or
unsubstituted cycloalkyl, substituted or unsubstituted
heterocycloalkyl, substituted or unsubstituted aryl, and
substituted or unsubstituted heteroaryl.
[0055] As used herein, the terms "heteroatom" or "ring heteroatom"
are meant to include, oxygen (O), nitrogen (N), sulfur (S),
phosphorus (P), Boron (B), Arsenic (As), and silicon (Si).
[0056] A "substituent group," as used herein, means a group
selected from the following moieties: [0057] (A) oxo, halogen,
--CF.sub.3, --CN, --OH, --NH.sub.2, --COOH, --CONH.sub.2,
--NO.sub.2, --SH, --SO.sub.2Cl, --SO.sub.3H, --SO.sub.4H,
--SO.sub.2NH.sub.2, --NHNH.sub.2, --ONH.sub.2,
--NHC.dbd.(O)NHNH.sub.2, --NHC.dbd.(O) NH.sub.2, --NHSO.sub.2H,
--NHC.dbd.(O)H, --NHC(O)--OH, --NHOH, --OCF.sub.3, --OCHF.sub.2,
unsubstituted alkyl, unsubstituted heteroalkyl, unsubstituted
cycloalkyl, unsubstituted heterocycloalkyl, unsubstituted aryl,
unsubstituted heteroaryl, and [0058] (B) alkyl, heteroalkyl,
cycloalkyl, heterocycloalkyl, aryl, and heteroaryl, substituted
with at least one substituent selected from: [0059] (i) oxo,
halogen, --CF.sub.3, --CN, --OH, --NH.sub.2, --COOH, --CONH.sub.2,
--NO.sub.2, --SH, --SO.sub.2Cl, --SO.sub.3H, --SO.sub.4H,
--SO.sub.2NH.sub.2, --NHNH.sub.2, --ONH.sub.2,
--NHC.dbd.(O)NHNH.sub.2, --NHC.dbd.(O) NH.sub.2, --NHSO.sub.2H,
--NHC.dbd.(O)H, --NHC(O)--OH, --NHOH, --OCF.sub.3, --OCHF.sub.2,
unsubstituted alkyl, unsubstituted heteroalkyl, unsubstituted
cycloalkyl, unsubstituted heterocycloalkyl, unsubstituted aryl,
unsubstituted heteroaryl, and [0060] (ii) alkyl, heteroalkyl,
cycloalkyl, heterocycloalkyl, aryl, and heteroaryl, substituted
with at least one substituent selected from: [0061] (a) oxo,
halogen, --CF.sub.3, --CN, --OH, --NH.sub.2, --COOH, --CONH.sub.2,
--NO.sub.2, --SH, --SO.sub.2Cl, --SO.sub.3H, --SO.sub.4H,
--SO.sub.2NH.sub.2, --NHNH.sub.2, --ONH.sub.2,
--NHC.dbd.(O)NHNH.sub.2, --NHC.dbd.(O) NH.sub.2, --NHSO.sub.2H,
--NHC.dbd.(O)H, --NHC(O)--OH, --NHOH, --OCF.sub.3, --OCHF.sub.2,
unsubstituted alkyl, unsubstituted heteroalkyl, unsubstituted
cycloalkyl, unsubstituted heterocycloalkyl, unsubstituted aryl,
unsubstituted heteroaryl, and [0062] (b) alkyl, heteroalkyl,
cycloalkyl, heterocycloalkyl, aryl, or heteroaryl, substituted with
at least one substituent selected from: oxo, halogen, --CF.sub.3,
--CN, --OH, --NH.sub.2, --COOH, --CONH.sub.2, --NO.sub.2, --SH,
--SO.sub.2Cl, --SO.sub.3H, --SO.sub.4H, --SO.sub.2NH.sub.2,
--NHNH.sub.2, --ONH.sub.2, --NHC.dbd.(O)NHNH.sub.2, --NHC.dbd.(O)
NH.sub.2, --NHSO.sub.2H, --NHC.dbd.(O)H, --NHC(O)--OH, --NHOH,
--OCF.sub.3, --OCHF.sub.2, unsubstituted alkyl, unsubstituted
heteroalkyl, unsubstituted cycloalkyl, unsubstituted
heterocycloalkyl, unsubstituted aryl, and unsubstituted
heteroaryl.
[0063] A "size-limited substituent" or "size-limited substituent
group," as used herein, means a group selected from all of the
substituents described above for a "substituent group," wherein
each substituted or unsubstituted alkyl is a substituted or
unsubstituted C.sub.1-C.sub.20 alkyl, each substituted or
unsubstituted heteroalkyl is a substituted or unsubstituted 2 to 20
membered heteroalkyl, each substituted or unsubstituted cycloalkyl
is a substituted or unsubstituted C.sub.3-C.sub.8 cycloalkyl, and
each substituted or unsubstituted heterocycloalkyl is a substituted
or unsubstituted 3 to 8 membered heterocycloalkyl.
[0064] A "lower substituent" or "lower substituent group," as used
herein, means a group selected from all of the substituents
described above for a "substituent group," wherein each substituted
or unsubstituted alkyl is a substituted or unsubstituted
C.sub.1-C.sub.8 alkyl, each substituted or unsubstituted
heteroalkyl is a substituted or unsubstituted 2 to 8 membered
heteroalkyl, each substituted or unsubstituted cycloalkyl is a
substituted or unsubstituted C.sub.3-C.sub.7 cycloalkyl, and each
substituted or unsubstituted heterocycloalkyl is a substituted or
unsubstituted 3 to 7 membered heterocycloalkyl.
[0065] In some embodiments, each substituted group described in the
compounds herein is substituted with at least one substituent
group. More specifically, in some embodiments, each substituted
alkyl, substituted heteroalkyl, substituted cycloalkyl, substituted
heterocycloalkyl, substituted aryl, substituted heteroaryl,
substituted alkylene, substituted heteroalkylene, substituted
cycloalkylene, substituted heterocycloalkylene, substituted
arylene, and/or substituted heteroarylene described in the
compounds herein are substituted with at least one substituent
group. In other embodiments, at least one or all of these groups
are substituted with at least one size-limited substituent group.
In other embodiments, at least one or all of these groups are
substituted with at least one lower substituent group.
[0066] In other embodiments of the compounds herein, each
substituted or unsubstituted alkyl may be a substituted or
unsubstituted C.sub.1-C.sub.20 alkyl, each substituted or
unsubstituted heteroalkyl is a substituted or unsubstituted 2 to 20
membered heteroalkyl, each substituted or unsubstituted cycloalkyl
is a substituted or unsubstituted C.sub.3-C.sub.8 cycloalkyl,
and/or each substituted or unsubstituted heterocycloalkyl is a
substituted or unsubstituted 3 to 8 membered heterocycloalkyl. In
some embodiments of the compounds herein, each substituted or
unsubstituted alkylene is a substituted or unsubstituted
C.sub.1-C.sub.20 alkylene, each substituted or unsubstituted
heteroalkylene is a substituted or unsubstituted 2 to 20 membered
heteroalkylene, each substituted or unsubstituted cycloalkylene is
a substituted or unsubstituted C.sub.3-C.sub.8 cycloalkylene,
and/or each substituted or unsubstituted heterocycloalkylene is a
substituted or unsubstituted 3 to 8 membered
heterocycloalkylene.
[0067] In some embodiments, each substituted or unsubstituted alkyl
is a substituted or unsubstituted C.sub.1-C.sub.8 alkyl, each
substituted or unsubstituted heteroalkyl is a substituted or
unsubstituted 2 to 8 membered heteroalkyl, each substituted or
unsubstituted cycloalkyl is a substituted or unsubstituted
C.sub.3-C.sub.7 cycloalkyl, and/or each substituted or
unsubstituted heterocycloalkyl is a substituted or unsubstituted 3
to 7 membered heterocycloalkyl. In some embodiments, each
substituted or unsubstituted alkylene is a substituted or
unsubstituted C.sub.1-C.sub.8 alkylene, each substituted or
unsubstituted heteroalkylene is a substituted or unsubstituted 2 to
8 membered heteroalkylene, each substituted or unsubstituted
cycloalkylene is a substituted or unsubstituted C.sub.3-C.sub.7
cycloalkylene, and/or each substituted or unsubstituted
heterocycloalkylene is a substituted or unsubstituted 3 to 7
membered heterocycloalkylene.
[0068] Certain compounds of the present invention possess
asymmetric carbon atoms (optical or chiral centers) or double
bonds; the enantiomers, racemates, diastereomers, tautomers,
geometric isomers, stereoisometric forms that may be defined, in
terms of absolute stereochemistry, as (R)- or (S)- or, as (D)- or
(L)- for amino acids, and individual isomers are encompassed within
the scope of the present invention. The compounds of the present
invention do not include those which are known in art to be too
unstable to synthesize and/or isolate. The present invention is
meant to include compounds in racemic and optically pure forms.
Optically active (R)- and (S)-, or (D)- and (L)-isomers may be
prepared using chiral synthons or chiral reagents, or resolved
using conventional techniques. When the compounds described herein
contain olefinic bonds or other centers of geometric asymmetry, and
unless specified otherwise, it is intended that the compounds
include both E and Z geometric isomers.
[0069] As used herein, the term "isomers" refers to compounds
having the same number and kind of atoms, and hence the same
molecular weight, but differing in respect to the structural
arrangement or configuration of the atoms.
[0070] The term "tautomer," as used herein, refers to one of two or
more structural isomers which exist in equilibrium and which are
readily converted from one isomeric form to another.
[0071] It will be apparent to one skilled in the art that certain
compounds of this invention may exist in tautomeric forms, all such
tautomeric forms of the compounds being within the scope of the
invention.
[0072] Unless otherwise stated, structures depicted herein are also
meant to include all stereochemical forms of the structure; i.e.,
the R and S configurations for each asymmetric center. Therefore,
single stereochemical isomers as well as enantiomeric and
diastereomeric mixtures of the present compounds, generally
recognized as stable by those skilled in the art, are within the
scope of the invention.
[0073] Unless otherwise stated, structures depicted herein are also
meant to include compounds which differ only in the presence of one
or more isotopically enriched atoms. For example, compounds having
the present structures except for the replacement of a hydrogen by
a deuterium or tritium, or the replacement of a carbon by .sup.13C-
or .sup.14C-enriched carbon are within the scope of this
invention.
[0074] The compounds of the present invention may also contain
unnatural proportions of atomic isotopes at one or more of the
atoms that constitute such compounds. For example, the compounds
may be radiolabeled with radioactive isotopes, such as for example
tritium (.sup.3H), iodine-125 (.sup.125I), or carbon-14 (.sup.14C).
All isotopic variations of the compounds of the present invention,
whether radioactive or not, are encompassed within the scope of the
present invention.
[0075] The symbol "" denotes the point of attachment of a chemical
moiety to the remainder of a molecule or chemical formula.
[0076] The terms "a" or "an," as used in herein means one or more.
In addition, the phrase "substituted with a[n]," as used herein,
means the specified group may be substituted with one or more of
any or all of the named substituents. For example, where a group,
such as an alkyl or heteroaryl group, is "substituted with an
unsubstituted C.sub.1-C.sub.20 alkyl, or unsubstituted 2 to 20
membered heteroalkyl," the group may contain one or more
unsubstituted C.sub.1-C.sub.20 alkyls, and/or one or more
unsubstituted 2 to 20 membered heteroalkyls.
[0077] Moreover, where a moiety is substituted with an R
substituent, the group may be referred to as "R-substituted." Where
a moiety is R-substituted, the moiety is substituted with at least
one R substituent and each R substituent is optionally different.
Where a particular R group is present in the description of a
chemical genus (such as Formula (I)), a Roman alphabetic symbol may
be used to distinguish each appearance of that particular R group.
For example, where multiple R.sup.13 substituents are present, each
R.sup.13 substituent may be distinguished as R.sup.13A, R.sup.13B,
R.sup.13C, R.sup.13D, etc., wherein each of R.sup.13A, R.sup.13B,
R.sup.13C, R.sup.13D, etc. is defined within the scope of the
definition of R.sup.13 and optionally differently.
[0078] Description of compounds of the present invention is limited
by principles of chemical bonding known to those skilled in the
art. Accordingly, where a group may be substituted by one or more
of a number of substituents, such substitutions are selected so as
to comply with principles of chemical bonding and to give compounds
which are not inherently unstable and/or would be known to one of
ordinary skill in the art as likely to be unstable under ambient
conditions, such as aqueous, neutral, and several known
physiological conditions. For example, a heterocycloalkyl or
heteroaryl is attached to the remainder of the molecule via a ring
heteroatom in compliance with principles of chemical bonding known
to those skilled in the art thereby avoiding inherently unstable
compounds.
[0079] A "reactive carbon," as used herein means, a carbon that is
reactive with fluoride in the presence of the transition metal
oxide.
[0080] In one aspect, a method is provided for forming an
[.sup.18F]-labeled organic compound in an aqueous medium. The
method includes combining within an aqueous medium an aqueous
[.sup.18F] fluoride, a transition metal oxide and an organic
compound precursor comprising a reactive carbon. An organic
compound is a carbon containing compound (e.g. containing a
substituted or unsubstituted alkyl, substituted or unsubstituted
heteroalkyl, substituted or unsubstituted aryl, substituted or
unsubstituted heteroaryl, substituted or unsubstituted cycloalkyl
or substituted or unsubstituted heterocycloalkyl). An organic
compound precursor is an organic compound that is utilized as a
reactant in the methods provided herein to produce an
[.sup.18F]-labeled organic compound. In embodiments, the organic
compound is less than about 1000 daltons. In embodiments, the
organic compound is less than about 900 daltons. In embodiments,
the organic compound is less than about 800 daltons. In
embodiments, the organic compound is less than about 700 daltons.
In embodiments, the organic compound is less than about 600
daltons. In embodiments, the organic compound is less than about
500 daltons. In embodiments, the organic compound is less than
about 400 daltons. In embodiments, the organic molecule is a drug
and/or modulator of a cellular process, such as a protein modulator
(e.g. kinase inhibitor). The aqueous [.sup.18F] fluoride source is
allowed to react with the reactive carbon thereby forming said
[.sup.18F]-labeled organic compound. In embodiments, the organic
compound precursor is an aryl organic compound precursor (i.e. an
organic compound comprising a substituted or unsubstituted aryl
moiety) and said [.sup.18F]-labeled organic compound is an
[.sup.18F]-labeled aryl organic compound (i.e. an
[.sup.18F]-labeled organic compound comprising an substituted or
unsubstituted aryl moiety).
[0081] The aqueous medium may be less than about 5%, 10%, 15%, 20%,
25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%,
90%, or 95% water. In embodiments, the aqueous medium may be less
than about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%,
60%, 65%, 70%, 75% water. In embodiments, the aqueous medium may be
less than about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%
water. In embodiments, the aqueous medium may be less than about
5%, 10%, 15%, 20% or 25% water. The [.sup.18F]-labeled organic
compound may be a positron emission tomography probe.
[0082] In embodiments, the reacting is SN2 nucleophilic
substitution reaction The reactive carbon may form part of a
substituted or unsubstituted aryl, substituted or unsubstituted
heteroaryl, substituted or unsubstituted alkyl, substituted or
unsubstituted heteroalkyl, substituted or unsubstituted cycloalkyl
or substituted or unsubstituted heterocycloalkyl. In embodiments,
the reactive carbon forms part of a substituted or unsubstituted
alkyl, substituted or unsubstituted heteroalkyl, substituted or
unsubstituted cycloalkyl or substituted or unsubstituted
heterocycloalkyl.
[0083] The transition metal oxide may be chromium(VI) oxide,
molybdenum(VI) oxide, platinum(IV) oxide, rhenium(VI) oxide,
rhenium(VII) oxide, ruthenium(IV) oxide, tantalum(V) oxide, tin(IV)
oxide, vanadium(IV) oxide, vanadium(V) oxide, yttrium(III) oxide,
zirconium(IV) oxide, chromium(III) oxide, bismuth(III) oxide,
manganese(IV) oxide, tungsten(IV) oxide, molybdenum(IV) oxide,
tungsten(VI) oxide, palladium(II) oxide, iron(II) oxide, zinc(II)
oxide, indium(III) oxide, copper(II) oxide, niobium(IV) oxide,
niobium(V) oxide, or titanium(IV) oxide.
[0084] In embodiments, the transition metal oxide is palladium(II)
oxide, iron(II) oxide, zinc(II) oxide, indium(III) oxide,
copper(II) oxide, niobium(IV) oxide, niobium(V) oxide, or
titanium(IV) oxide. The transition metal oxide may be TiO.sub.2,
NbO.sub.2, Nb.sub.2O.sub.5, In.sub.2O.sub.3, or CuO.
[0085] The aqueous medium may further include a base. The aqueous
medium may further include an ammonium base. In embodiments, the
aqueous medium further comprises an ammonium bicarbonate base.
[0086] The aqueous medium further comprises an alcohol co-solvent,
such as MeOH, EtOH, n-PrOH, i-PrOH, t-BuOH, tHexOH, n-octanol or
cyclohexanol. The alcohol co-solvent may be t-BuOH, tHexOH,
n-octanol or cyclohexanol.
[0087] The reactive compound or the organic compound precursor may
be attached to a tosylate moiety. In embodiments, the reactive
compound or the organic compound precursor is attached to a
tosylate moiety. In embodiments, the compound or the organic
compound precursor is attached to a benzenesulfonyl,
4-nitrobenzenesulfonyl (nosylate), methanesulfonyl (mesylate),
ethanesulfonyl, trifluoromethylsulfonyl (triflate), or
1,1,2,2,2-pentafluoroethane-1-sulfonyl moiety.
[0088] In embodiments the method is based on titania (titanium
dioxide, TiO.sub.2) nanoparticles (crystalline composition: 45%
rutile, 55% anatase; <200 nm size) as a catalyst. A nanoparticle
is particle having a longest dimension less than about 1 .mu.m
(e.g. less than about 200, 300, 400, 500, 600, 700, 800 or 900 nm).
The precursor solution is first incubated with the particles, and
then a mixture of phase-transfer agent and
[.sup.18F]fluoride/[.sup.18O]H.sub.2O (taken directly from
cyclotron-delivered vial or trapped and eluted from QMA-cartridge)
is added and reacted, followed by removal of the catalyst particles
by filtration and then purification and reformulation steps. The
use of TiO.sub.2 obviates the laborious synthesis and purification
of a metal-precursor complex prior to radiolabeling, and the method
is compatible with many commercially-available or
easily-synthesized precursors. We have demonstrated that this route
for radiofluorination is suitable for aromatic, aliphatic, and
cycloaliphatic precursors in organic-aqueous media with a tolerated
water content up to 25 vol %.
[0089] Titania is widely used in a variety of chemical processes,
including electro- and photochemistry. Along with broad catalytic
activity, it possesses a strong ability to adsorb water from
surrounding media. Numerous reports have demonstrated the mechanism
of water dissociation at titania surface, and we hypothesize that
this feature of TiO.sub.2 might be used for in situ desolvation of
[.sup.18F]fluoride from water to catalyze nucleophilic
radiofluorination reactions in organic-aqueous solutions without
preliminary drying of the [.sup.18F]fluoride. We present an
investigation of the influence of various reaction parameters on
the radiofluorination of a model PET probe precursor and also
discuss studies performed to further elucidate the mechanism of
TiO.sub.2-catalyzed radiofluorination.
EXAMPLES
General Information.
[0090] All the solvents and reagents were purchased from
Sigma-Aldrich Chemical Co. (St. Louis, Mo.), except for
Tetrabutylammonium bicarbonate (TBAB),
2,3-dimethoxy-5-[3-[[(4-methylphenyl)sulfonyl]oxy]propyl]-N-[[1-(-
2-propenyl-2-pyrrolidinyl)methyl] (tosyl-fallypride precursor),
1-(2,3-diacetyl-5-tosyl-(.alpha.-D-arabinofuranosyl)-2-nitroimidazole
(FAZA precursor), N-Boc-trans-4-tosyloxy-L-proline methyl ester
(trans-BTPME, cis-4-fluoroproline precursor) and the fallypride
standard compound were purchased from ABX Advanced Biochemical
Compounds (Radeberg, Germany).
[0091] No-carrier-added [.sup.18F]fluoride ion was obtained from
the UCLA Crump Institute for Molecular Imaging Cyclotron Facility
by irradiation of 85% .sup.18O-enriched water with an 11 MeV proton
beam using an RDS-112 cyclotron (Siemens Medical Solution,
Knoxville, Tenn.). Radioactivity was determined using a calibrated
ion chamber (Capintec CRC-15R). A radioactive thin layer
chromatography scanner (MiniGITA star) (Raytest USA, Inc,
Wilmington, N.C.) and an analytical-scale high performance liquid
chromatography (HPLC) system (Knauer, Germany) were used to analyze
radiofluorination efficiency. The analytical-scale HPLC used for
purification was equipped with a SecurityGuard C18 column
(Phenomenex, Torrance, Calif.), a Phenomenex Luna reversed-phase
C-18 column (250.times.4.6 mm), a variable wavelength UV detector
and a radiometric detector (Eckert & Ziegler, Washington D.C.,
USA). TLC mobile phase: acetonitrile-water 50:50. HPLC mobile
phase: acetonitrile-water 55:45.
Abbreviations
[0092] GCMS, gas-chromatography mass spectrometry; HPLC,
high-performance liquid chromatography; ICP-MS, inductively-coupled
plasma mass spectrometry; PET, positron-emission tomography; QC,
quality control; REE: radioactivity extraction efficiency; RCC,
radiochemical conversion; RCY, radiochemical yield; SA, specific
activity; TBAB, tetra-n-butylammonium bicarbonate; TBAF,
tetra-n-butylammonium fluoride; TLC, thin layer chromatography.
Example 1
[0093] As a model system for initial studies radiofluorination of
tosyl-fallypride 1 to [.sup.18F]fallypride 2, a highly specific
radioligand for positron-emission tomography of D.sub.2/D.sub.3
brain striatum receptors used in animal PET imaging to study the
brain conditions and functional malignancies was selected (M. R.
Javed, S. Chen, J. Lei, J. Collins, M. Sergeev, H.-K. Kim, C.-J.
Kim, R. M. van Dam, P. Y. Keng, Chem. Comm. 2014, 50, 1192-1194).
The synthetic procedure includes tetrabutylammonium bicarbonate
(TBAB), titania and 1:1 acetonitrile-thexyl alcohol solvent mixture
(Scheme 1). Ammonium bicarbonate base was used instead of inorganic
base/Cryptand due to its lower toxicity. According to Javed et al.,
(M. R. Javed, S. Chen, H.-K. Kim, L. Wei, J. Czernin, C.-J. Kim, R.
M. van Dam, P. Y. Keng, J. Nuc. Med. 2013, 55, 1-8.) addition of
thexyl alcohol is vital in fallypride radiosynthesis and improves
fluorination efficiency two-fold, thus the same two-component
organic medium was used. Experiments were performed at elevated
temperature using a computer-controlled Peltier heating system.
Fluorination efficiency was determined by radio-TLC and radio-HPLC.
Identity of radiofluorinated product was confirmed by co-injection
with [.sup.19F]fallypride (ABX GmbH, Germany). Radiochemical
conversions (RCCs) are presented as the mean of three runs.
##STR00001##
Example 2
[0094] Initial studies were performed to determine the necessity of
base for TiO.sub.2-catalyzed radiofluorination. Reactions were
performed in acetonitrile-thexyl alcohol (MeCN-tHexOH) medium with
or without base addition at 110.degree. C. for 7 min, the typical
conditions used in [.sup.18F]fallypride syntheses (M. R. Javed, S.
Chen, H.-K. Kim, L. Wei, J. Czernin, C.-J. Kim, R. M. van Dam, P.
Y. Keng, J. Nuc. Med. 2013, 55, 1-8.). Radioactivity was introduced
as 10 .mu.l of [.sup.18O]H.sub.2O/[.sup.18F]fluoride (typically
1.5-3 mCi). The amount of substrate 1 added was 2.3 .mu.mol, and
the total reaction volume was adjusted to 40 .mu.l. Without base
addition, the RCC was only 18%, but increased to 36% when TBAB was
used. Base-fluoride coupling may still be needed, possibly due to
better solubilization of in situ generated [.sup.18F]TBAF than
[.sup.18F]fluoride in organic-aqueous medium. Also it was revealed
that decay-corrected radioactivity recovery from the reaction
vessel, which includes unreacted fluoride and fluorinated product,
was less than 100%. After the reaction is done, the content of
reaction vial is extracted with methanol (2*200 .mu.l), and
combined extracts contained only .about.80% of initial
radioactivity. Further efforts to make extraction more effective
were not successful; thus we assumed some trapping of fluoride into
the solid-phase. During further experiments the percentage of
trapped fluoride remained remarkably constant at the level of
.about.20%. This loss is reflected in our reported RCCs, which we
calculate as: RCC=[radioactivity recovery in organic
extract]*[fluorinated product purity in organic extract].
Comparative experiments with dry [.sup.18F]TBAF without titania at
non-aqueous conditions led to 65% RCC; the `dry` reaction with
titania did not lead to fluoride conversion, organic extract
contained neither fluorinated product nor parent
[.sup.18F]fluoride, and all the radioactivity was counted in the
catalyst. This means that in non-aqueous medium TiO.sub.2 addition
results into total fluoride trapping, perhaps in the same manner as
was previously reported for SiO.sub.2 and Al.sub.2O.sub.3(S. S.
Tripathy, J.-L. Bersillon, K. Gopal, Sep. Purif Technol. 2006, 50,
310-317). Efforts to label the precursor in organic-aqueous
conditions without addition of titania failed, only unreacted
fluoride was detected.
Example 3
[0095] In the next set of studies, optimization of reaction
conditions was performed to determine tolerated water content
(Table 1) and optimal catalyst-precursor ratio (Table 3). The water
amount that leads to maximum [.sup.18F]fallypride RCC was found to
be <=25%, after which point a strong decrease in fluorination
was observed. It was revealed that catalyst-precursor ratio plays
important role not only in fluorination efficiency, but also
affects the radioactivity extraction. The optimal ratio of
TiO.sub.2 to precursor is 61:1 for the catalyst particle size
used.
Example 3.1: Evaluation of Water Content in Reaction Medium
##STR00002##
[0097] Procedure: A screw-cap scintillation vial (Fisherbrand
#03-339-22A) was loaded with TiO.sub.2 (0.14 mmol; crystalline
composition: 45% rutile, 55% anatase; <200 nm size) and
tosylated precursor 1a (2.3 .mu.mol) solution in pre-determined
amount (see Table 1) of 1:1 (v/v) mixture of acetonitrile (MeCN)
and thexyl alcohol (tHexOH). The aqueous solution of
[.sup.18F]F-TBAB was prepared by mixing equal volumes of
[.sup.18O]H.sub.2O/[.sup.18F] and 75 mM aqueous solution of TBAB. A
pre-determined volume (see Table 1) of this solution (containing
1.5-5 mCi radioactivity) was then added into reaction vial,
resulting into 0-62% water content in reaction mixture. The vial
was capped and transferred to computer-controlled Peltier heater.
Reaction was performed at 110.degree. C. for 7 minutes. The
reaction mixture was mixed by refluxing solvent; no active magnetic
stirring was used. After the reaction, the product was extracted
with methanol (2.times.200 .mu.L). Combined extracts were filtered
through Whatman `Anotop 10 Plus` filter (0.02 .mu.m) and
radiolabeled product content was analyzed by radio-TLC and
HPLC.
TABLE-US-00001 TABLE 1 Effect of water content on RCC. ACN- Water
Compound tHexOH [.sup.18F]/TBAB aq. content, 2a purity in RCC,
Entry volume, [.mu.L] volume, [.mu.L] [vol %] extract, [%] [%]
1.sup.a 40 0 0 0 0 2 38 2 5 80 .+-. 2 64 .+-. 2 3 36 4 10 81 .+-. 2
65 .+-. 2 4 34 6 15 81 .+-. 2 65 .+-. 3 5 30 10 25 81 .+-. 3 65
.+-. 1 6 26 14 35 64 .+-. 4 51 .+-. 3 7 20 20 50 36 .+-. 5 29 .+-.
4 8 18 22 55 20 .+-. 4 16 .+-. 2 9 15.2 24.8 62 0 0
.sup.a[.sup.18F]fluoride/TBAB complex was dried and reconstituted
in anhydrous acetonitrile before addition.
Example 3.1: Evaluation of Catalyst Loading
##STR00003##
[0099] It was found that the amount of catalyst added had a
substantial effect on RCC. Studies with different catalyst amounts
revealed that the optimal loading of TiO.sub.2 is 140 .mu.mol for
40 .mu.l reaction volume with 25 vol % water content for the
catalyst particle size used (<200 nm). This translates to
.about.60:1 ratio of catalyst to precursor 1 and enables production
of target compound 2 with the highest RCC (78%). The RCC drops for
both increasing and decreasing amounts of catalyst.
[0100] Procedure: A screw-cap scintillation vial was charged with
TiO.sub.2 (0.01-0.59 mmol) and tosylated precursor 1a (2.3 .mu.mol)
solution in 30 .mu.l of 1:1 mixture of acetonitrile and thexyl
alcohol. The aqueous solution of [.sup.18F]F-TBAB was prepared by
mixing equal volumes of [.sup.18O]H.sub.2O/[.sup.18F] and 75 mM
aqueous solution of TBAB. Aliquote of this solution (10 .mu.l,
containing 1.5-5 mCi radioactivity) was then added into reaction
vial, resulting into 25% water content in reaction mixture. The
vial was capped and transferred to computer-controlled Peltier
heater. Reaction was performed at 110.degree. C. for 7 minutes.
After the reaction is done, the product was extracted with methanol
(2.times.200 .mu.l). Combined extracts were filtered through
Whatman `Anotop 10 Plus` filter (0.02 .mu.m) and radiolabeled
product content was analyzed by radio-TLC and HPLC.
[0101] Looking at fluorination efficiency, we observed catalyst
amounts lower than the optimum to result in decreasing fluorination
efficiency, perhaps due to reduced desolvation of fluoride.
Surprisingly, increasing the amount of catalyst also decreased the
fluorination efficiency. Perhaps as the catalyst amount is
increased, one of the reaction components becomes depleted,
reducing the interactions necessary for fluorination.
[0102] On the other hand, looking at extraction efficiency, we
observed that REE decreases (i.e., trapping increases) with
increasing amount of catalyst. Due to this linear relation, we
suspect there are specific trapping sites for fluoride on the
TiO.sub.2, the number of which depends on the amount of catalyst
present. Perhaps trapping occurs via exchange of fluoride with
terminal hydroxyl groups (Minella, M.; Faga, M. G.; Maurino, V.;
Minero, C.; Pelizzetti, E.; Coluccia, S.; Martra, G. Langmuir 2010,
26, 2521; Minero, C.; Mariella, G.; Maurino, V.; Pelizzetti, E.
Langmuir 2000, 16, 2632; Minero, C.; Mariella, G.; Maurino, V.;
Vione, D.; Pelizzetti, E. Langmuir 2000, 16, 8964). The consistent
.about.20% trapping for a fixed amount of catalyst may represent
the equilibrium exchange between the surface and the reaction
solution containing both fluoride and hydroxide ions. The case of
100% trapping under dry conditions (Table 3, entry 6), where the
fluoride concentration dominates could represent a shift in this
equilibrium (Habuda-Stani , M.; Ravan{hacek over (c)}i{hacek over
(c)}, M.; Flanagan, A. Materials 2014, 7, 6317).
[0103] To determine if the optimal amount of catalyst is universal
or should be adjusted for every precursor, similar experiments were
performed with substrates 1i, 1q and 1t. The loading of 140 .mu.mol
of TiO.sub.2 remained optimal for these substrates as well (FIG.
19).
TABLE-US-00002 TABLE 3 Effect of catalyst loading on trapping and
RCC. Compound 2 Extraction [18F]- Catalyst, purity in extract,
efficiency, trapping, RCC, Entry [mmol] [%] [%] [%] [%] 1 0.01 2
.+-. 1 97 .+-. 2 3 .+-. 1 2 .+-. 1 2 0.06 23 .+-. 1 90 .+-. 2 10
.+-. 1 21 .+-. 1 3 0.09 36 .+-. 2 86 .+-. 2 14 .+-. 2 31 .+-. 2 4
0.14 85 .+-. 5 80 .+-. 2 20 .+-. 2 68 .+-. 3 5 0.25 39 .+-. 3 56
.+-. 2 44 .+-. 2 22 .+-. 1 6 0.37 21 .+-. 1 46 .+-. 2 54 .+-. 3 10
.+-. 1 7 0.59 7 .+-. 1 21 .+-. 2 79 .+-. 3 2 .+-. 1
Example 4
[0104] Optimal reaction time and temperature were determined as
well. Maximum RCC of 78% was achieved at 130.degree. C. with 10 min
reaction time.
Example 4.1: Evaluation of Temperature Profile
##STR00004##
[0106] Procedure: A screw-cap scintillation vial was charged with
TiO.sub.2 (0.01-0.59 mmol) and tosylated precursor 1 (2.3 .mu.mol)
solution in 30 .mu.l of 1:1 mixture of acetonitrile and thexyl
alcohol. The aqueous solution of [.sup.18F]F.sup.-/TBAB was
prepared by mixing equal volumes of [.sup.18O]H.sub.2O/[.sup.18F]
and 75 mM aqueous solution of TBAB. An aliquot of this solution (10
.mu.l, containing 1.5-5 mCi radioactivity) was then added into
reaction vial, resulting into 25% water content in reaction
mixture. The vial was capped and transferred to computer-controlled
Peltier heater. Reaction was performed at pre-determined
temperature for 7 minutes. After the reaction is done, the product
was extracted with methanol (2.times.200 .mu.l). Combined extracts
were filtered through Whatman `Anotop 10 Plus` filter (0.02 .mu.m)
and radiolabeled product content was analyzed by radio-TLC and
HPLC.
TABLE-US-00003 TABLE 4 Evaluation of temperature profile at 7 min
reaction time. Compound 2 Temperature, purity in extract, Entry
[.degree. C.] [%] RCC, [%] 1 50 0 0 2 80 18 .+-. 3 24 .+-. 1 3 110
60 .+-. 2 65 .+-. 2 4 130 85 .+-. 1 68 .+-. 4 5 140 86 .+-. 1 69
.+-. 3 7 145 86 .+-. 2 68 .+-. 2
Example 4.1: Evaluation of Time Profile at 130.degree. C.
##STR00005##
[0108] Procedure: A screw-cap scintillation vial (Fisherbrand
#03-339-22A) was loaded with TiO.sub.2 (0.01-0.59 mmol) and
tosylated precursor 1a (2.3 .mu.mol) solution in 30 .mu.L of 1:1
(v/v) mixture of acetonitrile and thexyl alcohol. The aqueous
solution of [.sup.18F]F.sup.-/TBAB was prepared by mixing equal
volumes of [.sup.18O]H.sub.2O/[.sup.18F] and 75 mM aqueous solution
of TBAB. An aliquot of this solution (10 .mu.L, containing 1.5-5
mCi radioactivity) was then added into reaction vial, resulting
into 25 vol % water content in reaction mixture. The vial was
capped and transferred to computer-controlled Peltier heater. The
reaction mixture was mixed by refluxing solvent; no active magnetic
stirring was used. Reaction was performed at 130.degree. C. for
pre-determined time period. After the reaction, the product was
extracted with methanol (2.times.200 .mu.L). Combined extracts were
filtered through Whatman `Anotop 10 Plus` filter (0.02 .mu.m) and
radiolabeled product content was analyzed by radio-TLC and
HPLC.
TABLE-US-00004 TABLE 5 Effect of reaction time on RCC. Reaction was
performed at 130.degree. C. Compound 2 purity in extract, RCC,
Entry Time, [min] [%] [%] 1 2 70 .+-. 3 56 .+-. 2 2 4 76 .+-. 1 61
.+-. 1 3 6 84 .+-. 2 67 .+-. 2 4 7 85 .+-. 1 68 .+-. 1 5 8 86 .+-.
1 69 .+-. 3 6 10 97 .+-. 3 78 .+-. 3 7 12 96 .+-. 1 77 .+-. 2
Example 4.2: Evaluation of Substrate-Catalyst Incubation Time
##STR00006##
[0110] Procedure: A screw-cap scintillation vial (Fisherbrand
#03-339-22A) was loaded with TiO.sub.2 (0.14 mmol) and tosylated
precursor 1a (2.3 .mu.mol) solution in 1:1 (v/v) mixture of
acetonitrile and thexyl alcohol (30 .mu.L). Vial was capped and
incubated at room temperature for a pre-determined time period. The
aqueous solution of [.sup.18F]F.sup.-/TBAB was prepared by mixing
equal volumes of [.sup.18]H.sub.2O/[.sup.18F] and 75 mM aqueous
solution of TBAB. An aliquot of this solution (10 .mu.L, containing
1.5-5 mCi radioactivity) was then added into pre-incubated reaction
vial, resulting into 25 vol % water content in reaction mixture.
The vial was capped and transferred to computer-controlled Peltier
heater. The reaction mixture was mixed by refluxing solvent; no
active magnetic stirring was used. Reaction was performed at
130.degree. C. for 10 minutes. After the reaction, the product was
extracted with methanol (2.times.200 .mu.L). Combined extracts were
filtered through Whatman `Anotop 10 Plus` filter (0.02 .mu.m) and
radiolabeled product content was analyzed by radio-TLC and
HPLC.
TABLE-US-00005 TABLE 6 Evaluation of radiofluorination time profile
after substrate-catalyst incubation. Compound 2 purity in Entry
Time, [min] extract, [%] RCC, [%] 1 1 42 .+-. 3 34 .+-. 2 2 2 61
.+-. 1 49 .+-. 1 3 3 87 .+-. 2 70 .+-. 2 4 4 91 .+-. 1 73 .+-. 1 5
5 96 .+-. 1 78 .+-. 3 6 6 97 .+-. 2 78 .+-. 3 7 7 96 .+-. 2 78 .+-.
3 8 8 97 .+-. 2 78 .+-. 3 9 10 96 .+-. 2 78 .+-. 3 10 12 96 .+-. 2
78 .+-. 3
TABLE-US-00006 TABLE 7 Effect of substrate-catalyst incubation time
on RCC. Compound 2a purity in extract, RCC, Entry Time, [min] [%]
[%] 1 0 85 .+-. 3 68 .+-. 2 2 5 85 .+-. 1 68 .+-. 1 3 10 85 .+-. 1
68 .+-. 1 4 15 85 .+-. 2 68 .+-. 2 5 30 89 .+-. 1 71 .+-. 1 6 45 92
.+-. 1 74 .+-. 3 7 60 98 .+-. 3 78 .+-. 3 8 75 98 .+-. 3 78 .+-. 3
9 90 98 .+-. 1 78 .+-. 2
Example 4.3: Studies of Solvent Effects
##STR00007##
[0112] Procedure: A screw-cap scintillation vial (Fisherbrand
#03-339-22A) was loaded with TiO.sub.2 (0.14 mmol) and tosylated
precursor 1a (2.3 .mu.mol) solution in a mixture of acetonitrile
and thexyl alcohol (30 .mu.L), including varying amounts of DMSO
(Table 8). Vial was capped and incubated at room temperature for 1
hour. The aqueous solution of [.sup.18F]F.sup.-/TBAB was prepared
by mixing equal volumes of [.sup.18O]H.sub.2O/[.sup.18F] and 75 mM
aqueous solution of TBAB. An aliquot of this solution (10 .mu.L,
containing 1.5-5 mCi radioactivity) was then added into
pre-incubated reaction vial, resulting into 25 vol % water content
in reaction mixture. The vial was capped and transferred to
pre-heated oil-bath. The reaction mixture was mixed by refluxing
solvent; no active magnetic stirring was used. Reaction was
performed at 130.degree. C. for 5 min. After the reaction is done,
the product was extracted with methanol (2.times.200 .mu.L).
Combined extracts were filtered through Whatman `Anotop 10 Plus`
filter (0.02 .mu.m) and radiolabeled product content was analyzed
by radio-TLC and HPLC.
TABLE-US-00007 TABLE 8 Effect of DMSO on extraction and RCC
Compound Precursor in 2a purity ACN/tHexOH, ACN/tHexOH, DMSO, DMSO,
in extract, Extraction # uL uL uL vol % [%] efficiency, % RCC, %
1.sup.a 15 15 0 0 98 .+-. 1 79 .+-. 1 77 .+-. 2 2 15 13 2 5 87 .+-.
3 59 .+-. 3 30 .+-. 3 3 15 10 5 12.5 77 .+-. 2 34 .+-. 2 18 .+-. 3
4 15 5 10 25 66 .+-. 1 23 .+-. 4 9 .+-. 1 5 15 0 15 37.5 41 .+-. 4
13 .+-. 1 1.2 .+-. 1 6.sup.b 0 30 75 0 3 .+-. 2 0 .sup.aStandard
experiment, reference point; .sup.bprecursor 1a was initially
dissolved in DMSO.
Example 4.4: Evaluation of Time Profile for Radiofluorination with
Pre-Incubation
##STR00008##
[0114] Procedure: A screw-cap scintillation vial was charged with
TiO.sub.2 (0.14 mmol) and tosylated precursor 1 (2.3 .mu.mol)
solution in 1:1 mixture of acetonitrile and alcohol (30 .mu.L).
Vial was capped and incubated at room temperature for 1 hour. The
aqueous solution of [.sup.18F]F.sup.-/TBAB was prepared by mixing
equal volumes of [.sup.18O]H.sub.2O/[.sup.18F] and 75 mM aqueous
solution of TBAB. Aliquot of this solution (10 .mu.l, containing
1.5-5 mCi radioactivity) was then added into pre-incubated reaction
vial, resulting into 25% water content in reaction mixture. The
vial was capped and transferred to computer-controlled Peltier
heater. Reaction was performed at 130.degree. C. for pre-determine
time-period. After the reaction is done, the product was extracted
with methanol (2.times.200 .mu.l). Combined extracts were filtered
through Whatman `Anotop 10 Plus` filter (0.02 .mu.m) and
radiolabeled product content was analyzed by radio-TLC and
HPLC.
TABLE-US-00008 TABLE 9 Evaluation of radiofluorination time profile
after substrate-catalyst incubation. Compound 2 purity in Entry
Time, [min] extract, [%] RCC, [%] 1 1 42 .+-. 3 34 .+-. 2 2 2 61
.+-. 1 49 .+-. 1 3 3 87 .+-. 2 70 .+-. 2 4 4 91 .+-. 1 73 .+-. 1 5
5 96 .+-. 1 78 .+-. 3 6 6 97 .+-. 2 78 .+-. 3 7 7 96 .+-. 2 78 .+-.
3 8 8 97 .+-. 2 78 .+-. 3 9 10 96 .+-. 2 78 .+-. 3 10 12 96 .+-. 2
78 .+-. 3
Example 4.5: Evaluation of Optimal Reaction Conditions
[0115] To maximize fluorination efficiency of the precursor 1a,
further evaluation of reaction conditions has been performed to
determine optimal reaction parameters.
[0116] The range of water content that provided maximum RCC was
found to be up to 25 vol %. In this aqueous range, the RCC and
fluoride trapping remained remarkably constant. With higher water
content, the trapping remained constant, but a strong decrease in
[.sup.18F]fluorination was observed. We hypothesize that higher
water content exceeds the capacity of the catalyst to adsorb and
split water, and thus the [.sup.18F]fluoride is not as effectively
desolvated, reducing the fluorination efficiency. If true, this
suggests that increased catalyst amount may enable improved water
tolerance if desired, but in light of results in the previous
section, it would also be necessary to increase the precursor
amount in the same proportion as the catalyst.
[0117] We also studied RCC as a function of reaction time and
temperature, to determine the optimal reaction time (5 min) and
temperature (130.degree. C.). The influence of the specific type of
alcohol co-solvent was evaluated as well. Several alcohols were
tested in place of thexyl alcohol, but relatively little difference
in RCC was observed. Thexyl alcohol showed the highest RCC of
alcohols tested.
Example 5
[0118] Comparative runs with other common drying agents, MgSO.sub.4
and CaCl.sub.2, were also performed, but no fluoride conversion
occurred (i.e. unreacted [.sup.18F]fluoride was detected as the
only radioactive component of reaction mixture), suggesting that
the role of TiO.sub.2 may not be merely water adsorption. Previous
reports show that oxo-containing species readily coordinate on a
TiO.sub.2 surface through hydrogen bonding..sup.[19,20] To explore
the role of coordination in enhancing the reaction, the
radiolabeling reaction was performed after incubation of tosylated
substrate with catalyst. When preliminary incubation of precursor
with titania was performed, significant decrease in reaction time
was observed. RCC of .about.70% was achieved in only 3 minutes and
maximum radiolabeling efficiency was reached in 5 minutes
(.about.77% RCC). Additional experiments on incubation time were
also performed. It was revealed that enhancement in reaction time
takes place only after at least 30 minutes of incubation and
reaches maximum at 60 minutes. No further improvement in fluoride
conversion was found after this point. These results suggest the
following mechanism of catalyzed fluorination: the tosylated
precursor binds to the catalyst through oxo-groups of sulfonyl
moiety during incubation step; when aqueous [.sup.18F]F.sup.-/TBAB
solution is added, aqueous solvate is adsorbed at active sites of
titania in water-dissociative mode with [.sup.18F]F.sup.- release;
ammonium base serves as fluoride-trapping agent and subsequently
conducts the phase-transfer of [.sup.18F]F-ion to
surface-coordinated precursor, where nucleophilic SN.sub.2-type
reaction occurs.
Example 6
[0119] The influence of different alcohols as co-solvents was also
evaluated (Table 3). No significant difference either in
radiolabeled product formation or in radioactivity extraction
efficiency was found for different alcohols as co-solvents, but
during the extraction step less swelling of oxide layer was
observed for higher boiling and more dense alcohols (thexyl
alcohol, cyclohexanol, n-octanol). In the case of smaller alcohols
(methanol, ethanol), titania sticking to glass was the most
extensive and the extraction process took longer time to achieve
maximum radioactivity extraction. Also it was observed that alcohol
structure does not influence the radioactivity extraction
efficiency, which was found to be .about.80% in all cases.
Example 6.1: Evaluation of Alcohol Co-Solvent Addition
##STR00009##
[0121] Procedure: A screw-cap scintillation vial (Fisherbrand
#03-339-22A) was loaded with TiO.sub.2 (0.14 mmol) and tosylated
precursor 1a (2.3 .mu.mol) solution in 1:1 (v/v) mixture of
acetonitrile and alcohol (30 .mu.L). Vial was capped and incubated
at room temperature for 1 hour. The aqueous solution of
[.sup.18F]F.sup.-/TBAB was prepared by mixing equal volumes of
[.sup.18O]H.sub.2O/[.sup.18F] and 75 mM aqueous solution of TBAB.
An aliquot of this solution (10 .mu.L, containing 1.5-5 mCi
radioactivity) was then added into pre-incubated reaction vial,
resulting into 25 vol % water content in reaction mixture. The vial
was capped and transferred to computer-controlled Peltier heater.
The reaction mixture was mixed by refluxing solvent; no active
magnetic stirring was used. Reaction was performed at 130.degree.
C. for pre-determine time-period. After the reaction, the product
was extracted with methanol (2.times.200 .mu.L). Combined extracts
were filtered through Whatman `Anotop 10 Plus` filter (0.02 .mu.m)
and radiolabeled product content was analyzed by radio-TLC and
HPLC.
TABLE-US-00009 TABLE 10 Evaluation of alcohol co-solvent..sup.[a]
Compound 2 purity in extract, RCC, Entry Alcohol [%] [%] 1 -- 0 0 2
MeOH 76 .+-. 3 61 .+-. 3 3 EtOH 85 .+-. 4 68 .+-. 3 4 n-PrOH 92
.+-. 5 74 .+-. 4 5 i-PrOH 83 .+-. 3 66 .+-. 3 6 t-BuOH 80 .+-. 4 64
.+-. 3 7 tHexOH 97 .+-. 2 78 .+-. 2 8 n-octanol 82 .+-. 4 66 .+-. 3
9 cyclohexanol 95 .+-. 1 76 .+-. 1 .sup.[a]Reaction conditions:
precursor 1 (2.3 .mu.mol) in acetonitrile-alcohol (1:1 mixture, 30
.mu.l), TiO.sub.2 (0.14 mmol); [.sup.18F]/TBAB aq. (10 .mu.l),
130.degree. C., 10 min.
Example 7
[0122] After establishing optimized reaction conditions, we next
investigated the generality of catalytic radiofluorination of
tosylated precursors. We synthesized a library of aromatic,
aliphatic and cycloaliphatic tosylates and tested them in
titania-catalyzed radiolabeling reactions along with commercially
available tosylated precursors of PET probes. The reaction turned
out to be highly efficient for low-molecular-weight precursors 3a-k
(RCC .about.80%), but resulted in low to moderate yields when bulky
and sterically hindered compounds 3l-n with additional oxo-moieties
were used. Perhaps lower yields in latter cases are due to
precursor coordination at the catalyst surface through other
oxo-groups instead of O.dbd.S.dbd.O moiety of tosyl, which results
in increased distance between [.sup.18F]F.sup.--ion at titania
surface and the tosylate reactive center.
Example 7.1: General Procedure for the Synthesis of Tosylated
Precursors 1B-u and 3a-k
##STR00010##
[0123] Tosylated precursors 1b-u were synthesized by general
procedure of Pasha et al. (Reddy, M. B. M.; Pasha, M. A.
Phosphorus, Sulfur, Silicon Relat. Elem. 2011, 186, 1867-1875; Kim,
D.-Y.; Kim, H.-J.; Yu, K.-H.; Min, J.-J. Bioconjugate Chem. 2012,
23, 431-437).
[0124] To a solution of corresponding starting alcohol (1.9 mmol)
in MeCN (10 mL) p-toluenesulfonyl chloride (2.2 mmol), and
Cs.sub.2CO.sub.3 (1 mol %), were added. The reaction mixture was
stirred rapidly at 25.degree. C. for 10 h. The progress of the
reaction was monitored by thin-layer chromatography (TLC). After
completion of the reaction, the mixture was diluted with water (20
mL) and product was extracted with diethyl ether (20 mL). The
organic extract was then washed with saturated solution of
NaHCO.sub.3 (2.times.10 mL), saline (2.times.10 mL) and water (10
mL). After drying over anhydrous Na.sub.2SO.sub.4, volatiles were
evaporated under reduced pressure, residue was dissolved in a
mixture of ethyl acetate:hexane 1:5 and purified via flash
chromatography over silica gel. Structure identity was confirmed by
.sup.1H and .sup.13C NMR spectroscopy, spectra were consistent with
literature data. Purity was established by RP-HPLC with C18-column
and a mixture of acetonitrile and water 55:45.
[0125] Precursors 1a, 1v, 1w and 1x were purchased from Advanced
Biochemical Compounds (ABX GMBH, Radeberg, Germany). Tosylates 3a-k
were prepared in an analogous fashion.
Example 7.2
[0126] General procedure for the synthesis of .sup.19F-fluorinated
standard compounds 4a-n-nonradioactive.
##STR00011##
[0127] .sup.19F-fluorinated standards for compounds 4a-n were
synthesized by general procedure of Kim et al.
[0128] To a solution of corresponding starting tosylated 3a-n (1
mmol) in MeCN (5 mL) 1M TBAF solution in THF (2 mmol) was added.
The reaction mixture was then heated at 85.degree. C. for 4 h.
Distilled water (10 ml) was added and the fluorinated product was
extracted with diethyl ether (2*10 ml). Organic extract was washed
with saturated solution of NaHCO.sub.3 (2*5 ml), saline (2*5 ml)
and water (5 ml). After dried over anhydrous Na.sub.2SO.sub.4
volatiles were evaporated under reduced pressure, residue was
dissolved in a mixture of ethyl acetate:hexane 1:5 and purified via
flash chromatography over silica gel. Structure identity was
confirmed by .sup.1H, .sup.13C, and .sup.19F NMR spectroscopy.
Purity was established by RP-HPLC with C18-column and a mixture of
acetonitrile and water 55:45.
TABLE-US-00010 TABLE 11 Substrate scope..sup.[a] ##STR00012## RCC
Entry Substrate 3.sup.[b] Product 4.sup.[c] [%] a ##STR00013##
##STR00014## 78 .+-. 3 b ##STR00015## ##STR00016## 80 .+-. 3 c
##STR00017## ##STR00018## 80 .+-. 2 d ##STR00019## ##STR00020## 80
.+-. 2 e ##STR00021## ##STR00022## 77 .+-. 4 f ##STR00023##
##STR00024## 80 .+-. 1 g ##STR00025## ##STR00026## 79 .+-. 2 h
##STR00027## ##STR00028## 80 .+-. 1 i ##STR00029## ##STR00030## 80
.+-. 2 j ##STR00031## ##STR00032## 80 .+-. 1 k ##STR00033##
##STR00034## 79 .+-. 1 l ##STR00035## ##STR00036## 70 .+-. 2 m
##STR00037## ##STR00038## 50 .+-. 4 n ##STR00039## ##STR00040## 26
.+-. 4
[a] Reaction conditions: precursor 3 (2.3 .mu.mol) in
acetonitrile-thexyl alcohol (1:1 mixture, 30 .mu.l) pre-incubated
with TiO.sub.2 (0.14 mmol) for 1 h; [.sup.18F]/TBAB aq. (10 .mu.l),
130.degree. C., 5 min. [b]Compounds 3a-k were synthesized according
to Reddy et al.(Reddy, M. B. M.; Pasha, M. A. Phosphorus, Sulfur,
Silicon Relat. Elem. 2011, 186, 1867-1875.), PET precursors 3l-m
were purchased from ABX GmbH, Germany. [c] .sup.19F-fluorinated
cold standards 4a-n were synthesized by method of Kim et al. (Kim,
D.-Y.; Kim, H.-J.; Yu, K.-H.; Min, J.-J. Bioconjugate Chem. 2012,
23, 431-437).
Example 7.3: General Procedure for Titania-Promoted
.sup.18F-Radiosynthesis of Compounds 4a-n
##STR00041##
[0130] Prior to use titanium dioxide was calcined at 550.degree. C.
during 12 h.
[0131] A screw-cap scintillation vial was charged with TiO.sub.2
(11.5 mg, 0.14 mmol) and tosylated precursor 3a-n (2.3 .mu.mol)
solution in 1:1 mixture of acetonitrile and thexyl alcohol (30
.mu.L). Vial was capped and incubated at room temperature for 1
hour. The aqueous solution of [.sup.18F]F.sup.-/TBAHCO.sub.3 (1.5-3
mCi, 10 .mu.l) was then added into pre-incubated vial, resulting
into 25% water content in reaction mixture. The vial was capped and
transferred to Peltier heater. Reaction was performed at
130.degree. C. for 5 minutes. After the reaction is done, the
product was extracted with methanol (2.times.200 .mu.l). Combined
extracts were thoroughly filtered through Whatman `Anotop 10 Plus`
filter (0.02 .mu.m) and radiolabeled product content was analyzed
by radio-TLC and HPLC.
Example 7.4: Optimized General Procedure for Titania-Catalyzed
.sup.18F-Radiosynthesis of Compounds 2a-x
##STR00042##
[0133] Prior to use titanium dioxide was calcined at 550.degree. C.
during 12 h.
[0134] A screw-cap scintillation vial (Fisherbrand #03-339-22A) was
loaded with TiO.sub.2 (11.5 mg, 0.14 mmol) and tosylated precursor
1a-x (2.3 .mu.mol) solution in 1:1 v/v mixture of acetonitrile and
thexyl alcohol (30 .mu.L). Vial was capped and incubated at room
temperature for 1 hour. The aqueous solution of
[.sup.18F]F.sup.-/TBAB was prepared by mixing equal volumes of
[.sup.18O]H.sub.2O/[F] and 75 mM aqueous solution of TBAB. The
aqueous solution of [.sup.18F]F.sup.-/TBAHCO.sub.3 (1.5-3 mCi, 10
.mu.L) was then added into pre-incubated vial, resulting into 25
vol % water content in reaction mixture. The vial was capped and
transferred to pre-heated oil bath. The reaction mixture was mixed
by refluxing solvent; no active magnetic stirring was used.
Reaction was performed at 130.degree. C. for 5 minutes. After the
reaction, the product was extracted with methanol (2.times.200
.mu.L). Combined extracts were thoroughly filtered through Whatman
`Anotop 10 Plus` filter (0.02 .mu.m) and radiolabeled product
content was analyzed by radio-TLC and HPLC. Radiolabeled compound
identity was established by co-injection with standard
.sup.19F-fluorinated compounds.
[0135] In conclusion, a method of TiO.sub.2 catalyzed
radiofluorination of tosylated precursors for preparation of
[.sup.18F]fluorine-labeled PET tracers was described. The suggested
method features a simple protocol utilizing wet [.sup.18F]fluoride
in a mixture with ammonium base without preliminary
drying-azeotroping step and in short reaction time. Nucleophilic
[.sup.18F]F-fluorination was shown to proceed in aqueous medium
with up to 25% water content with excellent radiolabeling
efficiency. The applicability of the reported protocol to a range
of tosylated substrates was also demonstrated for organic molecules
containing aromatic, aliphatic and cycloaliphatic moieties, and a
plausible mechanism of action is also suggested. Although
additional investigations are required to expand the scope and
further understand the mechanism and improve performance, high
radiofluorinating efficiency of this method may provide a versatile
tool for practitioners in the field of PET radiochemistry.
Example 8
[0136] To demonstrate the overall radiochemical yield of isolated
[.sup.18F]Fallypride 2a, we performed full production runs
(radiofluorination, HPLC purification, and formulation). The final
formulated product was obtained as a sterile, injectable solution.
During production, radioactivity measurements were recorded at key
steps to assess efficiency of each process and identify potential
areas for optimization (Table 12). The biggest loss is during
extraction from the catalyst (20% trapped) and an additional
.about.10% is lost during our purification and formulation
processes. Total production times, isolated yields and specific
activities are compared to those previously reported in literature
(Table 13). Generally, the isolated yield of titania-catalyzed
reaction tends to be higher than reported for macroscale automated
production, while it is comparable to microfluidic procedures, such
as syntheses on a digital microfluidic chip (Javed, M. R.; Chen,
S.; Lei, J.; Collins, J.; Sergeev, M.; Kim, H.-K.; Kim, C.-J.; Dam,
R. M. van; Keng, P. Y. Chem. Commun. 2014, 50, 1192). or using the
Advion Nanotek capillary reactor (Lu, S.; Giamis, A. M.; Pike, V.
W. Curr. Radiopharm. 2009, 2, 1). By avoiding the need for fluoride
drying/azeotroping, the synthesis process is simplified.
[0137] It is noteworthy to mention the high radiochemical purity of
target compound 2a that formed during reaction. Only two
radioactive peaks were detected by analytical HPLC, which consisted
of unreacted [.sup.18F]fluoride and the desired
[.sup.18F]Fallypride. Regarding HPLC analysis of the
non-radioactive side products, the hydroxylated compound, resulting
from hydrolysis, is clearly observed while no byproduct from
.beta.-elimination is apparent. With HPLC purification, the
[.sup.18F]fluoride and non-radioactive side products were
effectively removed, and the reformulated solution was then
examined by standard quality control (QC) tests (Keng, P. Y.; Chen,
S.; Ding, H.; Sadeghi, S.; Shah, G. J.; Dooraghi, A.; Phelps, M.
E.; Satyamurthy, N.; Chatziioannou, A. F.; Kim, C.-J.; van Dam, R.
M. Proc. Natl. Acad. Sci. 2012, 109, 690). to evaluation its
compliance with United States Food and Drug Administration
requirements for injectable PET tracers (Table 14).
TABLE-US-00011 TABLE 12 Titania-catalyzed production of
[.sup.18F]Fallypride..sup.a Parameter Run 1 Run 2 Run 3 Average
Initial 5.20 5.19 5.23 5.20 .+-. 0.02 activity, mCi REE, % 79.1
81.2 81.9 80.7 .+-. 1.5 RCC, % 79.1 81.2 81.5 80.6 .+-. 1.3 (non-
isolated) Activity 79.1 81.2 81.9 80.7 .+-. 1.5 remaining after
synthesis and extraction, %.sup.b Activity 75.7 76.5 77.6 76.6 .+-.
1.0 remaining after HPLC purification, %.sup.b Activity 71.2 68.6
73.2 71.0 .+-. 2.3 remaining after reformulation, %.sup.b Total
loss, % 28.8 31.4 26.8 28.9 .+-. 2.3 Isolated 71.2 68.6 73.2 71.0
.+-. 2.3 RCY, % .sup.aOptimized reaction conditions: 1 h
pre-incubation time; 2.3 .mu.mol of precursor; 140 .mu.mol of
TiO.sub.2; 40 .mu.l total reaction volume; no magnetic stirring;
radioactivity introduced as 10 .mu.l solution of aqueous
[.sup.18F]fluoride (~2.6 mCi) containing 0.36 .mu.mol of TBAB;
heated to 130.degree. for 5 min using an oil bath. For each run, 2
vials are pooled after extraction to improve accuracy of
measurements. .sup.bFractions of remaining radioactivity determined
by measuring the radioactivity after the relevant step, correcting
for decay, and dividing by the initial radioactivity.
TABLE-US-00012 TABLE 13 Comparison of catalytic production of 2a to
known procedures. Total Reactor Radiolabeling Mean time, Entry type
conditions RCY, % min Moon Macroscale, 100.degree. C., 30 min 68 74
et al., automated. 2010.sup.48 TracerLab FX Pike et Microscale,
150-190.degree. C., 16-88 50-218 al..sup.46 automated. 4-23 min
Nanotek Advion. Javed Microscale, 105.degree. C., 7 min 83 70 et
al..sup.7 automated. EWOD chip Lazari Macroscale 105.degree. C., 7
min 66 56.sup.a et al..sup.49 automated. Elixys .TM. Current Small-
130.degree. C., 5 min 71 50 report volume vial, manual .sup.aTotal
time reported without reformulation step
TABLE-US-00013 TABLE 14 Quality control tests of injectable
[.sup.18F]Fallypride solution. Clinical Clinical QC acceptance
Results of this test criteria study Optical Clear and Clear and
clarity particle free particle free pH 5.5-8.0 6.5 Radiochemical
>95% >99% purity Radiochemical Matches Matches identity
retention time retention time of the standard of the standard
.sup.18F- Half-life 105-115 min Half-life 111 min radionuclide
identity Endotoxin <5 EU/mL <1 EU/mL level Filter >50 psig
>100 psig integrity MeCN <410 ppm <2 ppm content Thexyl
<5000 ppm <1 ppm alcohol content Sterility No growth in No
growth in 14 14 days days Titanium None specified 36 .+-. 4 ng
content
[0138] With the introduction of the TiO.sub.2 catalyst into the
production procedure, an additional QC test to assess the titanium
content in the reformulated solution may be needed. While the 20 nm
filtration process and subsequent HPLC purification are expected to
eliminate all particles, there is still the possibility of titanium
ions in the final formulated solution. Using inductively-coupled
plasma mass spectrometry (ICP-MS), the titanium content in
representative samples was found to be 36.+-.4 ng (n=9) of titanium
per batch. Titanium is considered very inert and there do not
appear to be established limits for titanium in injectable
solutions. According to medicinal reports (Ipach, I.; Schafer, R.;
Mittag, F.; Leichtle, C.; Wolf, P.; Kluba, T. BMC Musculoskelet.
Disord. 2012, 13, 159; Patton, M. S.; Lyon, T. D. B.; Ashcroft, G.
P. Acta Orthop. 2008, 79, 820; Rodushkin, I.; Odman, F.; Branth, S.
Fresenius J. Anal. Chem. 1999, 364, 338), however, normal levels of
titanium in human body range from 0 to .about.20 .mu.g/L blood
(.about.0-100 .mu.g per whole body of an adult) in patients without
titanium implants, while reaching 100-150 ug/L blood (500-750 .mu.g
per whole body) in patients with artificial titanium joints. Thus,
an injection of formulated [.sup.18F]Fallypride produced by our
method would have a very miniscule impact because it contains
orders of magnitude less titanium than normally present in the
blood. This could suggest that routine titanium testing may not be
needed for every batch of injectable PET probe (Shao, X.; Schnau,
P. L.; Fawaz, M. V.; Scott, P. J. H. Nucl. Med. Biol. 2013, 40,
109; Radiopharmaceuticals for Position Emission
Tomography--Compounding. U.S. Pharmacopeial Convention, Chapter
823, USP 35-NF 50. 2012; pp 398-406).
[0139] We have, therefore, demonstrated the practical feasibility
of the newly developed synthetic approach to the synthesis of a
clinically-relevant PET probe, including compliance with FDA
requirements for injectable solutions in clinical applications. By
varying the precursor, other [.sup.18F]fluorine-labeled PET probes
could be produced by this procedure and similar QC results would be
expected.
##STR00043##
[0140] Procedure: Six screw-cap scintillation vials (Fisherbrand
#03-339-22A) were loaded with TiO.sub.2 (0.14 mmol) and tosylated
precursor 1a (2.3 .mu.mol) solution in 30 .mu.l of 1:1 (v/v)
mixture of acetonitrile and thexyl alcohol. The aqueous solution of
[.sup.18F]F.sup.-/TBAB was prepared by mixing equal volumes of
[.sup.18O]H.sub.2O/[.sup.18F] and 75 mM aqueous solution of TBAB.
10 .mu.l of this solution (containing 2.6 mCi radioactivity) was
then added into each reaction vial, resulting into 25 vol % water
content in reaction mixture. The vials were capped and transferred
to pre-heated oil bath. The reaction mixture was mixed by refluxing
solvent; no active magnetic stirring was used. Reaction was
performed at 130.degree. C. for 5 minutes. After the reaction is
done, the product from each vial was extracted with methanol
(2.times.200 .mu.L). For statistical purposes, pairs of organic
extracts were combined, giving 3 portions, each containing 800
.mu.L of organic extract.
[0141] Purification/reformulation process: Each combined organic
extract (800 .mu.L) was evaporated under stream of nitrogen in
plastic Eppendorf.RTM. tube using oil bath. Residue was
reconstituted in 90 .mu.L of HPLC buffer (55:45 v/v MeCN/aq.
ammonium formate+1% triethylamine) and purified via HPLC
(Phenomenex Luna reversed-phase C-18 column (250.times.4.6 mm)),
collecting peak at 12 min. Collected fraction (.about.2 ml) was
evaporated under stream of nitrogen in plastic Eppendorf.RTM. tube
using oil bath. Residue was reconstituted in DPBS buffer and
sterile filtered into sterile vial using Whatman Anotop 10 Plus
sterile filter (0.2 .mu.m). Resulting injectable solution underwent
usual set of QC tests, including determination of endotoxin level,
sterility, GCMS determination of residual solvents and ICP-MS
determination of titanium content. HPLC chromatogram of final
injectable solution and results of QC tests are shown below.
TABLE-US-00014 TABLE 15 Quality control tests of injectable
[.sup.18F]Fallypride solution. Clinical acceptance Clinical QC test
criteria Results of this study Optical clarity Clear and particle
free Clear and particle free pH 5.5-8.0 6.5 Radiochemical purity
>95% >99% Radiochemical Matches retention time of Matches
retention time identity the standard of the standard
.sup.18F-radionuclide Half-life 105-115 min Half-life 111 min
identity Endotoxin level <5 EU/mL <1 EU/mL Filter integrity
>50 psig >100 psig MeCN content <410 ppm <2 ppm Thexyl
alcohol <5000 ppm <1 ppm content Sterility No growth in 14
days No growth in 14 days Titanium content None specified 36 .+-. 4
ng
[0142] Javed, M. R.; Chen, S.; Lei, J.; Collins, J.; Sergeev, M.;
Kim, H.-K.; Kim, C.-J.; Dam, R. M. van; Keng, P. Y. Chem. Commun.
2014, 50, 1192.
Example 8.1: Characterization of Tosylate Precursors
##STR00044##
[0143] Phenyl p-toluenesulfonate (1b)
[0144] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.9-8.0 (d,
2H), 7.4 (d, J=8.1 Hz, 2H), 7.2-7.3 (m, 2H), 6.9-7.0 (m, 1H),
6.8-6.9 (m, 2H), 2.5 (s, 3H); .sup.13C NMR (100 MHz, CDCl.sub.3,
ppm) .delta. 155.4, 146.8, 141.6, 130.2, 129.6, 127.0, 120.8,
115.3, 21.8.
##STR00045##
Benzyl p-toluenesulfonate (1c)
[0145] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.91-7.96 (d,
2H), 7.39-7.44 (d, 2H), 7.38 (d, J=4.65 Hz, 4H), 7.28-7.34 (m, 1H),
4.70 (s, 2H), 2.50 (s, 3H); .sup.13C NMR (100 MHz, CDCl.sub.3, ppm)
.delta. 146.8, 141.7, 140.8, 130.2, 128.5, 127.6, 127.0, 126.9,
65.3, 21.8
##STR00046##
2-Phenylethyl p-toluenesulfonate (1d)
[0146] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.91-7.97 (d,
2H), 7.39-7.45 (d, 2H), 7.30-7.36 (m, 2H), 7.21-7.28 (m, 3H), 3.87
(t, J=6.60 Hz, 2H), 2.88 (t, J=6.60 Hz, 2H), 2.50 (s, 3H; .sup.13C
NMR (100 MH, CDCl.sub.3, ppm) .delta. 146.8, 141.7, 138.4, 130.2,
129.0, 128.5, 127.0, 126.4, 63.6, 39.2, 21.8.
##STR00047##
3-Phenylpropyl p-toluenesulfonate (1e)
[0147] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.91-7.97 (d,
2H), 7.39-7.44 (d, 2H), 7.27-7.33 (m, 2H), 7.17-7.24 (m, 3H), 3.69
(t, J=6.36 Hz, 2H), 2.69-2.76 (m, 2H), 2.50 (s, 3H), 1.86-1.96 (m,
2H; .sup.13C NMR (100 MHz, CDCl.sub.3, ppm) .delta. 146.8, 141.8,
130.2, 128.4, 128.3, 127.0, 125.8, 62.2, 34.2, 32.0, 21.8.
##STR00048##
6-Phenylhexyl p-toluenesulfonate (1g)
[0148] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.90-7.97 (d,
2H), 7.39-7.45 (d, 2H), 7.25-7.32 (m, 2H), 7.15-7.22 (m, 3H), 3.64
(t, J=6.60 Hz, 2H), 2.58-2.67 (m, 2H), 2.50 (s, 3H), 1.53-1.73 (m,
4H), 1.30-1.45 (m, 4H); .sup.13C NMR (100 MHz, CDCl.sub.3, ppm)
.delta. 146.8, 142.7, 141.7, 130.2, 128.3, 128.2, 127.0, 125.6,
62.9, 35.8, 32.6, 31.4, 29.0, 25.6, 21.8.
##STR00049##
Naphth-1-yl p-toluenesulfonate (1h)
[0149] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 8.18-8.24 (m,
1H), 7.91-7.97 (d, 2H), 7.80-7.87 (m, 1H), 7.49-7.54 (m, 2H), 7.46
(d, J=8.31 Hz, 1H), 7.38-7.43 (d, 2H), 7.33 (dd, J=7.46, 8.19 Hz,
1H), 6.84 (dd, J=0.98, 7.58 Hz, 1H), 2.49 (s, 3H); .sup.13C NMR
(100 MHz, CDCl.sub.3, ppm) .delta. 151.3, 146.8, 141.6, 134.7,
130.2, 127.6, 127.0, 126.4, 125.8, 125.2, 124.3, 121.5, 120.6,
108.6, 21.8, 15.
##STR00050##
Naphth-2-yl p-toluenesulfonate (1i)
[0150] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.91-7.97 (d,
2H), 7.74-7.81 (m, 2H), 7.69 (dd, J=0.61, 8.19 Hz, 1H), 7.45 (ddd,
J=1.22, 6.91, 8.25 Hz, 1H), 7.41 (d, J=0.61, 8.68 Hz, 2H), 7.35
(ddd, J=1.22, 6.91, 8.25 Hz, 1H), 7.09-7.18 (m, 2H), 2.49 (s, 3H);
.sup.13C NMR (100 MHz, CDCl.sub.3, ppm) .delta. 153.3, 146.8,
141.6, 134.6, 130.2, 129.8, 128.9, 127.7, 127.0, 126.5, 126.3,
123.6, 117.7, 109.5, 21.8.
##STR00051##
1-Phenylethyl p-toluenesulfonate (1j)
[0151] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.90-7.95 (d,
2H), 7.39-7.44 (d, 2H), 7.33-7.39 (m, 4H), 7.24-7.31 (m, 1H), 4.90
(q, J=6.36 Hz, 1H), 2.50 (s, 3H), 1.50 (d, J=6.60 Hz, 3H); .sup.13C
NMR (100 MHz, CDCl.sub.3, ppm) .delta.
##STR00052##
Octyl p-toluenesulfonate (1k)
[0152] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.90-7.95 (d,
2H), 7.38-7.44 (d, 2H), 3.64 (t, J=6.60 Hz, 2H), 2.50 (s, 3H),
1.52-1.62 (m, 2H), 1.21-1.40 (m, 10H), 0.85-0.92 (m, 3H); .sup.13C
NMR (100 MHz, CDCl.sub.3, ppm) .delta. 146.8, 141.7, 130.2, 127.0,
63.0, 32.8, 31.8, 29.4, 29.2, 25.7, 22.6, 21.8, 14.1.
##STR00053##
Cyclohexyl p-toluenesulfonate (1l)
[0153] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.87-7.97 (d,
2H), 7.41 (d, J=8.07 Hz, 2H), 3.60 (td, J=4.68, 8.99 Hz, 1H), 2.49
(s, 3H), 1.46-1.98 (m, 5H), 1.06-1.36 (m, 5H); .sup.13C NMR (100
MHz, CDCl.sub.3, ppm) .delta. 146.8, 141.7, 130.2, 127.0, 114.9,
70.3, 35.5, 25.4, 24.1, 21.
##STR00054##
m-cresyl p-toluenesulfonate (1n)
[0154] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.67-7.77 (m,
2H), 7.32 (d, J=8.07 Hz, 2H), 7.10-7.18 (m, 1H), 7.05 (d, J=7.58
Hz, 1H), 6.87 (s, 1H), 6.66-6.76 (m, 1H), 2.46 (s, 3H), 2.30 (s,
3H); .sup.13C NMR (100 MHz, CDCl.sub.3, ppm) .delta. 149.9, 145.5,
140.3, 132.9, 130.0, 129.5, 128.8, 128.1, 123.3, 119.4, 77.6, 77.3,
22.0, 21.5.
##STR00055##
p-ethylphenyl p-toluenesulfonate (1o)
[0155] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.64-7.77 (m,
2H), 7.25-7.36 (m, 2H), 7.02-7.14 (m, 2H), 6.82-6.94 (m, 2H), 2.61
(q, J=7.58 Hz, 2H), 2.45 (s, 3H), 1.21 (t, J=7.58 Hz, 3H); .sup.13C
NMR (100 MHz, CDCl.sub.3, ppm) .delta. 147.6, 145.2, 143.1, 132.6,
129.7, 128.8, 128.5, 122.1, 77.3, 76.7, 28.2, 21.7, 15.3.
##STR00056##
p-ethoxycarbonylphenyl p-toluenesulfonate (1p)
[0156] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.91-8.06 (m,
2H), 7.63-7.76 (m, 2H), 7.32 (dd, J=0.49, 8.56 Hz, 2H), 7.01-7.12
(m, 2H), 4.36 (q, J=7.09 Hz, 2H), 2.45 (s, 3H), 1.38 (t, J=7.21 Hz,
3H); .sup.13C NMR (100 MHz, CDCl.sub.3, ppm) .delta. 165.5, 152.9,
145.7, 132.1, 131.3, 129.9, 129.3, 128.5, 122.3, 115.0, 77.4, 77.0,
76.7, 61.3, 21.8, 14.3.
##STR00057##
p-nitrophenyl p-toluenesulfonate (1q)
[0157] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 8.10-8.25 (m,
2H), 7.65-7.79 (m, 2H), 7.36 (d, J=8.07 Hz, 2H), 7.13-7.23 (m, 2H),
2.48 (s, 3H); .sup.13C NMR (100 MHz, CDCl.sub.3, ppm) .delta.
153.6, 145.9, 131.4, 129.8, 128.2, 125.1, 122.9, 76.7, 76.4,
21.4.
##STR00058##
p-cyanophenyl p-toluenesulfonate (1r)
[0158] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 7.68-7.78 (m,
2H), 7.57-7.66 (m, 2H), 7.35 (d, J=8.07 Hz, 2H), 7.08-7.20 (m, 2H),
2.47 (s, 3H); .sup.13C NMR (100 MHz, CDCl.sub.3, ppm) .delta.
152.6, 146.1, 133.9, 131.9, 130.1, 128.5, 123.5, 117.7, 115.0,
111.2, 77.4, 77.0, 76.7, 21.8.
##STR00059##
pyridin-2-yl p-toluenesulfonate (1s)
[0159] .sup.1H NMR (400 MHz, CDCl.sub.3, ppm) .delta. 8.43-8.53 (m,
1H), 8.15 (d, J=1.71 Hz, 1H), 7.63-7.76 (m, 2H), 7.42-7.52 (m, 1H),
7.33 (d, J=8.07 Hz, 2H), 7.25-7.31 (m, 1H), 2.45 (s, 3H); .sup.13C
NMR (100 MHz, CDCl.sub.3, ppm) .delta. 148.5, 146.8, 146.3, 144.3,
132.0, 130.5, 130.3, 128.8, 124.5, 77.6, 77.3, 22.0.
[0160] References to NMR spectra of .sup.19F-labeled compounds.
[0161] 2a: Kim, K.; Miller, N. R.; Sulikowski, G. A.; Lindsley, C.
W. Bioorg. Med. Chem. Lett. 2008, 18(16), 4467. [0162] 2b, 2q, 2s:
Forlani, L.; Mezzina, E. Bioorg. J. Chem. Soc. Perkin Trans. 2
1995, 11, 2019. [0163] 2c: Ochiai, M.; Yoshimura, A.; Hoque, Md.
M.; Okubo, T.; Saito, M.; Miyamoto, K. Org. Lett., 2011, 13 (20),
5568. [0164] 2d, 2k, 2l: Koroniak, H.; Walkowiak, J.; Grys, K.;
Rajchel, A.; Alty, A.; Du Boisson, R. J. Fluorine Chem. 2006,
127(9), 1245. [0165] 2e: Beaulieu, F.; Beauregard, L.-P.;
Courchesne, G.; Couturier, M.; LaFlamme, F.; L'Heureux, A. Org.
Lett. 2009, 11 (21), 5050. [0166] 2f, 2g: Prakash, G. K. S.;
Chacko, S.; Vaghoo, H.; Shao, N.; Gurung, L.; Mathew, T.; Olah, G.
A. Org. Lett. 2009, 11 (5), 1127. [0167] 2h, 2p: Tang, P.; Ritter,
T. Tetrahedron 2011, 67(24), 4449. [0168] 2i: Cassidei, L.;
Sciacovelli, O. Spectrochim. Acta A-M. 1985, 41(12), 1459. [0169]
2j: Jindrich, J.; Dvorakova, H.; Holy, A. Collect. Czech. Chem.
Commun. 1992, 57, 1466. [0170] 2m: Tang, P.; Wang, W.; Ritter, T.
J. Am. Chem. Soc., 2011, 133 (30), 11482. [0171] 2n: Kruger, T.;
Vorndran, K.; Linker, T. Chem. Eur. J. 2009, 15, 12082. [0172] 2o:
Gieshoff, T. N.; Villa, M.; Welther, A.; Plois, M.; Chakraborty,
U.; Wolf, R.; von Wangelin, A. J. Green Chem. 2015, 17, 1408.
[0173] 2r: Enthaler, S. Chem. Eur. J. 2011, 17, 9316 [0174] 2t:
Chambers, R. D.; Parsons, M.; Sandford, G.; Skinner, C. J.;
Atherton, M. J.; Moilliet, J. S. J. Chem. Soc. Perkin Trans. 1
1999, 7, 803. [0175] 2u: Ple, N.; Turck, A.; Heynderickx, A.;
Queguiner, G. Tetrahedron 1998, 54(19), 4899. [0176] 2v: Bejot, R.;
Fowler, T.; Carroll, L.; Boldon, S.; Moore, J. E.; Declerck, J.;
Gouverneur, V. Angew. Chem. Int. Ed. 2008, 48, 586. [0177] 2w:
Kumar. P.; Wiebe, L. I.; Asikoglu, M.; Tandon, M.; McEwan, A. J. B.
Appl. Radiat. Isotopes 2002, 57(5), 697. [0178] 2x: Graham, T. J.
A.; Lambert, R. F.; Ploessl, K.; Kung, H. F.; Doyle, A. G. J. Am.
Chem. Soc. 2014, 136(14), 5291.
Example 8
[0179] General procedure for titania-catalyzed
[.sup.18F]-radiofluorination: A screw-cap scintillation vial was
charged with TiO.sub.2 (0.14 mmol) and tosylated precursor (2.3
.mu.mol) solution in 1:1 mixture of acetonitrile and thexyl alcohol
(30 .mu.L). Vial was capped and incubated at room temperature for 1
hour. The aqueous solution of [.sup.18F]F.sup.-/TBAB was prepared
by mixing equal volumes of [.sup.18O]H.sub.2O/[.sup.18F] and 75 mM
aqueous solution of TBAB. An aliquot of this solution (10 .mu.l,
containing 1.5-3 mCi radioactivity) was then added into
pre-incubated reaction vial, resulting in 25% overall water content
in reaction mixture. The vial was capped and transferred to
computer-controlled Peltier heater. The reaction was performed at
130.degree. C. for 5 minutes. After the reaction, the product was
extracted with methanol (2.times.200 .mu.l). Combined extracts were
filtered through Whatman `Anotop 10 Plus` filter (0.02 .mu.m) and
radiolabeled product content was analyzed by radio-TLC and
HPLC.
Example 8.2 Determination of Specific Activity
[0180] High specific activity (SA) of PET tracers is essential to
minimize the injected quantity of the non-radioactive form of the
tracer, which can saturate rare biological targets, such as
neurological receptors, and subsequently lower the image quality
and possibly cause pharmacologic effects..sup.55 It has been
confirmed that SA plays an important role in PET image
quality,.sup.29,56,57 especially in small animals..sup.58,59 Using
standard methods.sup.7, the SA for TiO2 catalyzed synthesis of
[.sup.18F]Fallypride 2a was found to be 5.+-.2 Ci/.mu.mol (n=5).
This is higher than typically obtained from macroscale synthesis.
(0.4-3 Ci/.mu.mol)..sup.49,60 This evidence suggests TiO.sub.2
catalysis could be successfully used for routine production of PET
imaging probes that require high SA.
Example 8.3: Scale-Up Synthesis
[0181] Previous experiments utilized operating volumes of 40 .mu.l,
10 .mu.L of which was [.sup.18F]fluoride solution. While we have
been able to demonstrate the production of several millicuries of
the isolated product starting from .about.5 mCi of
[.sup.18F]fluoride, it may be desirable in some cases to produce
larger amounts of product (e.g., for clinical production), which
requires a larger volume of the initial [.sup.18F]fluoride
solution.
[0182] One simple way to scale up the quantity of tracer produced
is to run several reactions in parallel and pool the results;
however, this would require multiple reaction vessels and may not
be convenient to handle or automate. Another approach is to scale
up the reaction volume, enabling a larger volume of
[.sup.18F]fluoride to be used while still keeping water content
within the 25 vol % range, and thus enabling larger amount of
starting radioactivity. To test this possibility, we explored
proportionally increasing the amounts of all of the reaction
components (i.e., precursor, TiO.sub.2, solvent, and aqueous
[.sup.18F]fluoride/TBAB solution). As an example, the catalytic
fluorination of 1a was scaled up to a factor of 3, such that the
final volume of the reaction mixture comprised 120 .mu.l. During
these experiments, we found that 5 min reaction time was
insufficient to efficiently fluorinate the precursor (fluorination
efficiency=50%). With increased heating time, it was possible to
increase fluorination efficiency to the values seen prior to
scaling (FIG. 5). We suspect that longer time is needed for
sufficient diffusive mixing in the larger volume. We also
encountered some initial difficulties during the filtration step to
remove the nanoparticles after the reaction was done. We observed
clogging of the 20 nm filter due to the increased amount of
TiO.sub.2. This issue was resolved by incorporating an initial
pre-filtration step with a 0.22 .mu.m filter prior to 20 nm fine
filtering. Unfortunately, this had the effect of slightly reducing
the extraction efficiency, from 80.+-.2% to 71.+-.13% (FIG.
21).
[0183] The tested scale-up factor of 3 is sufficient for production
of a human-dose of [.sup.18F]Fallypride, and further increases in
scale are presumably possible, if desired; with higher volumes,
stirring during the pre-incubation and reaction steps may become
important, requiring additional optimization of reaction time and
extraction procedures. Another reason to perform volume scale-up is
to potentially enable automation in commercially-available
radiosynthesizers, which typically require at least several hundred
microliters of solution in the reaction. Though there are
advantages in performing reactions in extremely small
volumes,.sup.7,8 it will be some time before automated and
commercialized versions of such technologies are widely
available.
[0184] As an alternative way to increase the amount of
radioactivity in the reaction without impacting reaction volume,
solid phase extraction procedures using microscale QMA cartridges
could be used to concentrate the [.sup.18F]fluoride to obtain
higher starting radioactivity in volumes of the
[.sup.18F]fluoride/TBAB solution described here (i.e. 10 .mu.L
water content). Several reports have shown that an entire cyclotron
target volume can be trapped and efficiently eluted in only 5-45
.mu.L of eluent solution..sup.61-63 This would likely be the
preferred approach to scale-up the amount of radioactivity since no
increase in reaction volume would be necessary.
Example 8.4 Substrate Scope
[0185] In order to explore the utility of the TiO.sub.2 catalytic
approach for the synthesis of other PET tracers, we investigated
the scope of applicable substrates. We first considered the use of
other leaving groups with sulfonyl moieties (i.e., triflate and
nosylate). Examples of additional leaving groups may be
benzenesulfonyl, 4-methylbenzenesulfonyl (tosylate),
4-nitrobenzenesulfonyl (nosylate), methanesulfonyl (mesylate),
ethanesulfonyl, trifluoromethylsulfonyl (triflate), or
1,1,2,2,2-pentafluoroethane-1-sulfonyl. Surprisingly, the
radiofluorination of commercially available substrates 6 and 7
(precursors for 2'-deoxy-2'-[.sup.18F]fluoro-D-glucose
([.sup.18F]FDG), and 3'-deoxy-3'-[.sup.18F]fluoro-L-thymidine
([.sup.18F]FLT)) (FIG. 22) resulted in RCC=0%.
[0186] In a presence of the catalyst, triflate and nosylate groups
seemed to become overreactive, and immediate explosive hydrolysis
was observed upon aqueous [.sup.18F]fluoride addition. When
analyzed, only unreacted [.sup.18F]fluoride and hydroxylated
compounds 6-OH and 7-OH were detected. This phenomenon suggests
that reactivity of oxygen-containing leaving groups are increased
when incubated with TiO.sub.2. Due to this additional activation,
the ideal leaving group should initially possess lower reactivity
(tosyloxy preferred before triflyloxy or nosyloxy), otherwise
concurrent side-reaction of hydrolysis prevails over
[.sup.18F]fluorination.
[0187] We next investigated the generality of TiO.sub.2-catalyzed
radiofluorination of tosylated precursors. A library of aromatic,
aliphatic and cycloaliphatic tosylates was tested, along with the
commercially available tosylated PET probe precursors for
[.sup.18F]-4-fluoroproline ([.sup.18F]-4-FP),
[.sup.18F]-fluoroazomycin-arabinoside ([.sup.18F]FAZA) and
[.sup.18F]-fluoroerythronitroimidazole ([.sup.18F]FETNIM) (Table
6). The methodology was highly efficient for low-molecular-weight
precursors 1b-v (65-80% RCC) but resulted in low to moderate yields
with bulky and sterically hindered substrates 1w-x (i.e., from the
commercially available precursors for [.sup.18F]FAZA and
[.sup.18F]FETNIM, respectively). These particular precursors also
contain additional oxo-moieties, which potentially lower yields by
coordinating the precursor at the catalyst surface instead of at
the O.dbd.S.dbd.O moiety of the tosylate leaving group. Such
coordination could significantly reduce the [.sup.18F]fluoride
interaction with the tosylate reactive center by placing the
reaction center further from the catalyst surface where fluoride
desolvation occurs. We are currently looking into methods to
further understand the reaction mechanism to predict the
effectiveness of different substrates and perhaps enable improved
substrate design.
TABLE-US-00015 TABLE 16 Substrate scope for the TiO.sub.2 catalyzed
radiofluorination of tosylated substrates.sup.a. ##STR00060##
##STR00061## 2b (78 .+-. 3% RCC) ##STR00062## 2c (80 .+-. 3% RCC)
##STR00063## 2d (80 .+-. 2% RCC) ##STR00064## 2e (80 .+-. 2% RCC)
##STR00065## 2f (77 .+-. 4% RCC) ##STR00066## 2g (80 .+-. 1% RCC)
##STR00067## 2h (79 .+-. 2% RCC) ##STR00068## 2i (80 .+-. 1% RCC)
##STR00069## 2j (80 .+-. 2% RCC) ##STR00070## 2k (80 .+-. 1% RCC)
##STR00071## 2l (79 .+-. 1% RCC) ##STR00072## 2m (74 .+-. 2% RCC)
##STR00073## 2n (76 .+-. 1% RCC) ##STR00074## 2o (65 .+-. 2% RCC)
##STR00075## 2p (78 .+-. 4% RCC) ##STR00076## 2q (79 .+-. 2% RCC)
##STR00077## ##STR00078## 2r (79 .+-. 2% RCC) ##STR00079## 2s (70
.+-. 7% RCC) ##STR00080## 2t (70 .+-. 2% RCC) ##STR00081## 2u (68
.+-. 5% RCC) ##STR00082## 2v (70 .+-. 2% RCC) ##STR00083## 2w (50
.+-. 4% RCC) ##STR00084## 2x (26 .+-. 4% RCC) .sup.aOptimized
reaction conditions: 1 h pre-incubation time; 2.3 .mu.mol of
precursor; 140 .mu.mol of TiO.sub.2; 130.degree. C., 5 min; 40
.mu.l total reaction volume; no magnetic stirring; radioactivity
introduced as 10 .mu.l solution of aqueous [.sup.18F]fluoride
(1.5-4 mCi) containing 0.36 .mu.mol TBAB. For all entries, REE was
observed to be ~80%.
[0188] In conclusion, we have developed a novel method of
TiO.sub.2-catalyzed radiofluorination of tosylated precursors and
demonstrated its use for the preparation of .sup.18F-labeled PET
probes. The method avoids the need for drying of the
[.sup.18F]fluoride/[.sup.18O]H.sub.2O from the cyclotron before
fluorination. The wet [.sup.18F]fluoride is mixed with a phase
transfer agent and added to a solution of precursor solution
pre-incubated with TiO2 nanoparticles and reacted for a short time.
In this fashion, nucleophilic .sup.18F-fluorination is shown to
proceed rapidly and efficiently in aqueous medium with up to 25 vol
% water content, which to the best of our knowledge is the highest
reported other than enzymatic methods. We have also demonstrated
the production of clinically-relevant amounts of
[.sup.18F]Fallypride with this approach as well as shown compliance
of the final formulated PET tracer with QC requirements for
clinical use. The product was found to have high specific activity
even with low amounts of starting radioactivity. The applicability
of the reported protocol to a range of tosylated substrates was
also demonstrated for organic molecules containing aromatic,
aliphatic and cycloaliphatic moieties. Although extensive
additional investigations are required to explore the substrate
scope and further understand the mechanism, we anticipate that the
facile procedure and high radiofluorination efficiency of this new
method may provide a versatile tool for practitioners in the field
of PET radiochemistry. Based on our hypothesized mechanism of
reaction, further studies regarding the importance of the structure
of the precursor and other effective catalysts are currently in
progress in our group.
Example 9
[0189] A panel of 25 TMOs in powder form (.ltoreq.200 nm particle
size), were screened in the radiofluorination of tosyl-fallypride
in a mixed aqueous-organic medium. Equal parts of
[.sup.18O]H.sub.2O/[.sup.18F]fluoride and aqueous 75 mM
tetrabutylammonium hydrocarbonate (TBAB) were mixed, added to a
one-hour pre-incubated solution of TMO and tosyl-fallypride in
acetonitrile and 2,3-dimethyl-2-butanol (1:1 v/v), and then reacted
at 130.degree. C. for 5 min in a closed container. The final
reaction mixture contained 20% water. Catalyst and substrate scope
are further explored in the radiolabeling of an array of tosylated
PET-precursors.
[0190] No fluoride conversion of tosyl-fallypride took place using
oxides of Mo, Pt, Re, Ru, Ta, Sn, V and Y, nor for the absence of
catalyst altogether. Low fluoride conversion (2-14%) was observed
for Zr, Bi, Mn, Mo, Cr and W oxides. Moderate fluorine conversion
(45-49%) was observed for Pd, Fe and Zn oxides. The best
decay-corrected [.sup.18F]fallypride radiochemical yields,
comparable to those previously found for TiO.sub.2 (78%), were
obtained for In.sub.2O.sub.3 (65%), CuO (80%), NbO.sub.2 (76%) and
Nb.sub.2O.sub.5 (85%). These latter catalysts were applied to
fluorination of other substrates: FAZA-precursor (5-50%),
cis-FPro-precursor (4-70%), FETNIM-precursor (8-42%) and
FET-precursor (70-73%).
[0191] Catalytic activity of TMOs towards radiofluorination in
highly aqueous media was demonstrated. The radiolabeling was
directly performed with aqueous [.sup.18F]fluoride without the
drying/azeotroping step with 20% water content in the reaction
mixture. Thus, radiosynthesis time was significantly reduced while
still maintaining high fluoride conversion. The general
applicability of the synthetic strategy to an array of PET probes
from tosylated precursors was demonstrated.
REFERENCES
[0192] M. R. Javed et al., .sub.Chem. Comm. 2014, 50, 1192-1194; M.
Sergeev et al., "Titania-catalyzed [.sup.18F]-radiofluorination of
tosylated precursors in highly aqueous media", Manuscript in
preparation.
TABLE-US-00016 [0192] TABLE 17 FAZA-precursor TiO.sub.2, 50 .+-. 3%
(n = 3) Nb.sub.2O.sub.5, 16 .+-. 1% (n = 3) cis-FPro-precursor
TiO.sub.2, 70 .+-. 4% (n = 3) Nb.sub.2O.sub.5, 28 .+-. 1% (n = 3)
FETNIM-precursor TiO.sub.2, 26 .+-. 1% (n = 3) Nb.sub.2O.sub.5, 42
.+-. 2% (n = 3) FET-precursor N/A Nb.sub.2O.sub.5, 73 .+-. 4% (n =
3)
List of Screened Substrates and Decay-Corrected Yields Comparing
the Use of TiO.sub.2 and Nb.sub.2O.sub.5 Catalysts
TABLE-US-00017 TABLE 18 Transition metal oxides screening in
radiofluorination of tosylfallypride. Product Radio-Purity
Extraction # Catalyst in Extract (%) Efficiency RCC, % 1
chromium(VI) oxide 0 2 molybdenum(VI) oxide 0 3 platinum(IV) oxide
0 4 rhenium(VI) oxide 0 5 rhenium(VII) oxide 0 6 ruthenium(IV)
oxide 0 7 tantalum(V) oxide 0 8 tin(IV) oxide 0 9 vanadium(IV)
oxide 0 10 vanadium(V) oxide 0 11 yttrium(III) oxide 0 12
zirconium(IV) oxide 56.12 2.7 1.52 13 chromium(III) oxide 34.19 5.4
1.85 14 bismuth(III) oxide 9.38 22.8 2.14 15 manganese(IV) oxide
7.26 31.7 2.30 16 tungsten(IV) oxide 9.13 35.5 3.24 17
molybdenum(IV) oxide 24.93 23.9 5.96 18 tungsten(VI) oxide 43.39
32.1 13.92 19 palladium(II) oxide 55.49 80.7 44.78 20 iron(II)
oxide 73.22 64.4 47.15 21 zinc(II) oxide 71.9 67.6 48.59 22
indium(III) oxide 90.96 71.4 64.97 23 copper(II) oxide 93.37 80.3
74.99 24 niobium(IV) oxide 89.92 84.7 76.20 25 niobium(V) oxide
95.33 85.3 81.31 Ref titanium(IV) oxide 80 78
TABLE-US-00018 TABLE 19 Transition metal oxide-catalyzed
radiofluorination of tosylated PET-precursors. Values are
decay-corrected radiochemical yields (%) and represented as an
average of 3 experiments. Precursor Catalyst 1 2 3 4 5 TiO2 78 .+-.
4 50 .+-. 3 70 .+-. 4 26 .+-. 1 -- NbO2 76 .+-. 4 7 .+-. 1 9 .+-. 1
8 .+-. 1 70 .+-. 4 Nb2O5 81 .+-. 4 16 .+-. 1 28 .+-. 1 42 .+-. 2 73
.+-. 4 In2O3 65 .+-. 3 5 .+-. 1 4 .+-. 1 9 .+-. 1 -- CuO 75 .+-. 4
12 .+-. 1 11 .+-. 1 34 .+-. 2 --
[0193] Precursors: [0194] 1.
2,3-dimethoxy-5-[3-[[(4-methylphenyl)sulfonyl]
oxy]propyl]-N-[[1-(2-propenyl-2-pyrrolidinyl)methyl]
(tosyl-fallypride), fallypride precursor [0195] 2.
1-(2,3-diacetyl-5-tosyl-(.alpha.-D-arabinofuranosyl)-2-nitroimidazole,
FAZA precursor [0196] 3. N-Boc-trans-4-tosyloxy-L-proline methyl
ester (trans-BTPME), cis-4-fluoroproline precursor [0197] 4.
(4R-trans)-2,2-dimethyl-5-[(2-nitro-1H-imidazol-1-yl)methyl]-1,3-dioxolan-
e-4-methanol 4-methylbenzenesulfonate, FETNIM precursor [0198] 5.
(2S)--O-(2'-tosyloxyethyl)-N-trityl-tyrosine-tert-butyl ester, FET
precursor
Example 9.1
[0199] Based on titania catalyzed reaction results, a new set of
transition metal oxides was tested in reaction of
radiofluorination. The model reaction used is the conversion of
tosyl-fallypride to .sup.18F-fallypride. Results of oxide-catalyst
screening are compared to those previously found for TiO.sub.2
catalysis.
TABLE-US-00019 TABLE 19.1 # Name Purity in Extract (%) Extracted
Activity Trapped Activity Extr. Eff RCC, % 1 chromium(VI) oxide 0
n/a n/a 0.0 0 2* molybdenum(VI) oxide 0 n/a n/a 0.0 0 3
platinum(IV) oxide 0 n/a n/a 0.0 0 4* rhenium(VI) oxide 0 n/a n/a
0.0 0 5* rhenium(VII) oxide 0 n/a n/a 0.0 0 6 ruthenium(IV) oxide 0
n/a n/a 0.0 0 7 tantalum(V) oxide 0 n/a n/a 0.0 0 8 tin(IV) oxide 0
n/a n/a 0.0 0 9* vanadium(IV) oxide 0 n/a n/a 0.0 0 10* vanadium(V)
oxide 0 n/a n/a 0.0 0 11 yttrium(III) oxide 0 n/a n/a 0.0 0
[0200] With these catalysts, low yields of Fallypride were obtained
using conditions established for Titania catalysis. Radioactivity
extraction efficiency suffers with these catalysts, which
inherently leads to low RCC. More thorough investigation of
reaction conditions is planned to investigate whether these oxides
could be applicable for radiofluorination reactions.
TABLE-US-00020 TABLE 19.2 # Name Purity in Extract (%) Extracted
Activity Trapped Activity Extr. Eff RCC, % 1 zirconium(IV) oxide
56.12 5 180 2.7 1.52 2 chromium(III) oxide 34.19 11 192 5.4 1.85 3
bismuth(III) oxide 9.38 31 105 22.8 2.14 4 manganese(IV) oxide 7.26
51 110 31.7 2.30 5 tungsten(IV) oxide 9.13 44 80 35.5 3.24 6
molybdenum(IV) oxide 24.93 43 137 23.9 5.96 7 tungsten(VI) oxide
43.39 43 91 32.1 13.92
[0201] With these catalysts, moderate yields of Fallypride were
obtained using conditions established for Titania catalysis.
Extraction efficiency is comparable to titania-catalyzed reaction
when Pd oxide was used, but moderate for Fe and Zn catalysts. More
thorough investigation of reaction conditions is planned to
investigate whether these oxides can be applicable for
radiofluorination reactions.
TABLE-US-00021 TABLE 19.3 # Name Purity in Extract (%) Extracted
Activity Trapped Activity Extr. Eff RCC, % 1 palladium(II) oxide
55.49 138 33 80.7 44.78 2 iron(II) oxide 73.22 123 68 64.4 47.15 3
zinc(II) oxide 71.9 196 94 67.6 48.59
[0202] For these catalysts, high yields of Fallypride were obtained
using conditions established for Titania catalysis. Good extraction
efficiency was also observed in all cases. These four catalysts
have been further investigated for radiolabeling reaction
efficiency at different conditions.
TABLE-US-00022 TABLE 19.4 Purity in Extract # Name (%) Extracted
Activity Trapped Activity Extr. Eff RCC, % 1 indium(III) oxide
90.96 140 56 71.4 64.97 2 copper(II) oxide 93.37 155 38 80.3 74.99
3 niobium(IV) oxide 89.92 150 27 84.7 76.20 4 niobium(V) oxide
95.33 145 25 85.3 81.31
A summary chart is shown below:
[0203] Preliminary results indicated promising results for these
catalysts so experiments were repeated. Statistical data set for
In(III), Nb(IV), Nb(V) and Cu(II) catalyzed fallypride formation is
shown and compared to titania. Results are repeatable as evidenced
by a narrow standard deviation.
TABLE-US-00023 TABLE 19.6 Oxide Extraction RCC, % TiO2 80 .+-. 2 78
.+-. 2 In2O3 72 .+-. 4 65 .+-. 5 NbO2 80 .+-. 5 80 .+-. 5 Nb2O5 85
.+-. 3 85 .+-. 5 CuO 80 .+-. 4 75 .+-. 5
Transition metal oxides screening: 130 C, 5 min.
Example 9.2
[0204] Investigation on temperature profile was performed. It was
found that T-optimum for four oxides of interest is the same as for
Titania. Plateau was achieved at 130.degree. C.; no obvious RCC
increase is found beyond this point. This temperature is used for
further reactions.
[0205] Time profiles were also collected. It was revealed that the
optimal time for all these reactions is 5 min, after which point no
substantial change in RCC was found. It was noted that in case of
Cu, Nb(IV) and Nb(V) oxides that the reaction can be terminated
after 3 minutes without significant loss in RCC, while In-catalyzed
reaction shows substantial increase in RCC between 3 and 5
minutes.
With these conditions, new set of reactions was performed in order
to determine the specific activity of radiolabeled fallypride.
Reference reaction (not using catalytic method) was performed with
a standard procedure using dried/azeotroped fluoride in microchip
synthesis (FIGS. 23 and 24).
TABLE-US-00024 TABLE 19.7 Run Specific Activity (Ci/.mu.mol)
Non-catalytic method performed on 4.5 microchip TiO.sub.2 4.6
In.sub.2O.sub.3 4 NbO.sub.2 5.7 Nb.sub.2O.sub.5 5.9 CuO 5.9
[0206] Specific activity in newly-developed synthesis was found to
be comparable with standard (non-catalytic) preparation method. No
significant difference was observed when 5 oxides under
investigation were used. This adds one more advantage to our
invention as we can synthesize PET tracers with high specific
activity, even starting with low radioactivity.
[0207] A set of ABX substrates for commercial PET tracer synthesis
was tested for applicability in oxide-catalyzed synthesis. It was
shown that fallypride is synthesized with high efficiency in all
cases, while it was impossible to detect FHBG or FETA formation in
any reaction. FAZA and BTPME precursors were found to be less
preferable substrates for In, Nb and Cu oxides compared to
TiO.sub.2, while FETNIM precursor was more effectively fluorinated
with Nb(V) oxide than with Titania. No FET formation was found in
case of Ti, Cu and In oxides, but surprisingly high RCC was
observed when niobium oxides are used.
[0208] Currently we assume that transition metal in oxide catalyst
and the precursor undergo the intermediate complex formation which
is further fluorinated. Deeper investigation of precursor
architecture and transition metal is planned for further steps of
our research.
Example 10
[0209] We performed a series of experiments (Table 1) to confirm
the importance of each species in the reaction. Entries 1 and 2
show the conventional synthesis conditions where [.sup.18F]fluoride
is pre-dried and reaction takes place in anhydrous organic media.
The improvement in RCC due to addition of thexyl alcohol is
apparent. Entry 5 shows 68% RCC resulting from catalytic synthesis
conditions with all species included as described above.
Comparative runs without the phase transfer catalyst resulted in
only 18% RCC. Thus, the phase transfer agent appears to be
important as well, possibly due to better solubilization of in situ
generated tetra-n-butylammonium fluoride ([.sup.18F]TBAF), compared
to [.sup.18F]fluoride, in organic-aqueous media. As expected,
experiments in the absence of catalyst did not lead to formation of
desired product 2a in organic-aqueous media (Entry 3), indicating
that TiO.sub.2 is essential when there is water in the reaction
mixture. If the [.sup.18F]fluoride is dried (as in conventional
synthesis) prior to catalytic reaction, no conversion was observed
(Entry 6). In fact, the filtrate contained neither fluorinated
product nor parent [.sup.18F]fluoride; all the radioactivity was
found bound to the catalyst. This means that in non-aqueous media,
TiO.sub.2 addition results in total [.sup.18F]fluoride trapping
(REE 0%). On the other hand, REE was found to be remarkably
constant (.about.80%) for all of the TiO.sub.2 catalyzed conditions
containing water. Even if the reaction was performed without the
precursor, the REE was unchanged (80.+-.2%).
[0210] The influence of the type of phase-transfer agent was
evaluated by carrying out the reaction with
K.sub.2CO.sub.3/K.sub.222 mixture (Entry 7). This resulted in a
substantial decrease in RCC suggesting that TBAB is a superior
phase transfer agent for these reactions.
[0211] Finally, to assess whether the role of TiO.sub.2 was simply
to sequester water to facilitate fluorination in mixed
aqueous-organic media, comparative runs with particles of other
common non-oxide drying agents, MgSO.sub.4 and CaCl.sub.2 (140
.mu.mol each), were also performed (Entries 9-10). These showed
zero RCC, suggesting an effect of TiO.sub.2 beyond simple water
adsorption, but most probably its ability of water splitting.
TABLE-US-00025 TABLE 20 Influence of reaction components on
formation of 2a..sup.a Phase transfer MeCN, Thexyl Water, #
Catalyst agent.sup.b .mu.l alcohol, .mu.l .mu.l.sup.c REE, % RCC, %
1 none TBAB 40 0 0 100.sup.d 31 .+-. 2 2 none TBAB 20 20 0
100.sup.d 64 .+-. 4 3 none None 15 15 10 100.sup.d 0 4 TiO.sub.2
None 15 15 10 79 .+-. 4 18 .+-. 3 5 TiO.sub.2 TBAB 15 15 10 80 .+-.
3 68 .+-. 2 6 TiO.sub.2 TBAB 20 20 0 0 0 7 TiO.sub.2
K.sub.2CO.sub.3/ 15 15 10 78 .+-. 3 39 .+-. 6 K.sub.222 8 none
K.sub.2CO.sub.3/ 20 20 0 100.sup.d 31 .+-. 4 K.sub.222 9 MgSO.sub.4
TBAB 15 15 10 99 .+-. 1 0 10 CaCl.sub.2 TBAB 15 15 10 99 .+-. 1 0
.sup.aReactions were performed with 2.3 .mu.mol 1a, 140 .mu.mol
TiO.sub.2 in 40 .mu.L reaction volume at 110.degree. C. for 7 min
without magnetic stirring. .sup.bAmounts of phase transfer agent
used, when applicable: 0.36 .mu.mol TBAB; 0.36 .mu.mol
K.sub.2CO.sub.3 and 0.36 .mu.mol K.sub.222. .sup.cFor cases where
water is 0 .mu.L, [.sup.18F]fluoride added as dry complex with
phase-transfer agent (1.5-4 mCi) reconstituted in 10 .mu.l of
MeCN-thexyl alcohol (1:1 v/v); for other cases, radioactivity
introduced as solution of aqueous [.sup.18F]fluoride (1.5-4 mCi)
containing phase-transfer agent; .sup.d In case of catalyst absence
no extraction performed.
Example 11
[0212] Hypothesized mechanism of TiO.sub.2-catalyzed
radiofluorination: Previous reports show that oxo- and
oxy-containing species readily coordinate on a TiO.sub.2 surface
through hydrogen bonding..sup.32-35 Thus, we hypothesize that in
addition to an interaction with water, the TiO.sub.2 catalyst could
also serve to coordinate tosyl-Fallypride 1a via oxygen atoms of
the sulfonyl group, facilitating reaction with desolvated
[.sup.18F]fluoride in close proximity. Based on these ideas, the
following mechanism of catalyzed fluorination is suggested (FIG.
19).
[0213] Hydrogen bonding occurs between oxygen atoms of the sulfonyl
moiety and TiO.sub.2, which coordinates tosylated precursor to the
surface of the catalyst; when aqueous [.sup.18F]fluoride/TBAB
solution is added, solvated [.sup.18F]fluoride is adsorbed at
active sites of TiO.sub.2 where the aqueous shell is split
resulting in [.sup.18F]fluoride release (i.e., activation); TBAB
phase transfer catalyst then serves as a
[.sup.18F]fluoride-trapping agent and intercepts activated
[.sup.18F]fluoride, subsequently conducting the phase-transfer of
[.sup.18F]fluoride to the surface-coordinated precursor to
facilitate the SN.sub.2-type reaction. Because the coordination
with the precursor is at the leaving group, the resulting
radiofluorinated product is released upon formation from the
TiO.sub.2.
[0214] Evidence for coordination: To explore the role of
coordination in the reaction mechanism, we performed radiolabeling
after first incubating the tosylated substrate with catalyst. If
coordination indeed occurs, prolonged exposure of the precursor to
the catalyst should increase the amount of precursor bound to the
surface of the catalyst and thus promote increased
SN.sub.2-reactions (i.e., radiolabeling efficiency). Thus, a
solution of tosyl-Fallypride 1a in 1:1 (v/v) MeCN-thexyl alcohol
was added to the catalyst and incubated at room temperature for
various durations. After incubation, aqueous
[.sup.18F]fluoride/TBAB mixture was added, and radiolabeling was
performed by heating at 110.degree. C. for 12 min using an oil
bath. The reaction mixture was mixed by refluxing solvent; no
magnetic stirring was used. We observed a modest enhancement in RCC
starting after 20-30 min of incubation and reaching a maximum
improvement after .about.1 hr.
[0215] Analytical samples of organic solution after incubation with
catalyst contained significant amount of precursor 1a; thus, it is
likely that the observed saturation is due to occupation of all
accessible active sites of TiO.sub.2 capable of binding the
oxygen-atoms of the leaving group. Attempts to perform
pre-incubation at elevated temperatures (30, 45 and 60.degree. C.)
showed similar results, i.e., the timescale was not shortened. It
should be noted that the pre-incubation step was performed before
the introduction of [.sup.18F]fluoride; therefore, incorporation of
pre-incubation into the synthesis protocol does not introduce any
delays that would affect the yield due to decay.
[0216] Studies were performed by running the radiofluorination
reaction in the presence of various amounts of a non-reactive
SO-containing compound (dimethylsulfoxide, DMSO) to assess whether
the presence of another co-coordinating species could block the
binding of the precursor and lower the RCC
[0217] It was revealed that even slight addition of DMSO
dramatically affected the RCC; 2-fold decrease in RCC was
registered at 5 vol % DMSO with nearly complete inhibition at 37.5
vol % DMSO, suggesting that DMSO molecules may indeed bind to
active sites of TiO.sub.2, thus reducing sites available for
precursor coordination. Surprisingly, the REE was also
significantly affected, and the amount of [.sup.18F]fluoride
trapped onto the catalyst increased with increasing DMSO content.
Almost total [.sup.18F]fluoride trapping (90%) was registered at 75
vol % DMSO. This suggests that instead of merely affecting
precursor coordination, DMSO may interact with the catalyst in
additional ways leading to trapping of fluoride, such as DMSO-water
cluster formation,.sup.36-39 intercalation of DMSO-water clathrate
inside the oxide structure,.sup.40 or DMSO-induced creation of
positively-charged sites..sup.41
[0218] To investigate further the need for leaving group
coordination at the TiO.sub.2 surface, experiments were performed
comparing tosylated compounds 1b, 1c and 1s with their brominated
versions 3-5 (not suspected to coordinate with surface) in
TiO.sub.2-catalyzed [.sup.18F]fluorination (Table 21). No product
was observed in case of bromo-derivatives, while high RCCs of
.about.80% were determined for tosylated precursors, which agrees
with the necessity for the proposed oxygen-coordinating mechanism
at the leaving group. The REE in case of bromo-substituted
substrates remained close to 80%, i.e., similar to that for
tosylated reactants.
TABLE-US-00026 TABLE 21 TiO.sub.2 catalyzed radiofluorination of
tosylated vs. brominated substrates.sup.a. Entry Structure 1
##STR00085## ##STR00086## 1b 3 (78 .+-. 3% RCC) (0% RCC) 2
##STR00087## ##STR00088## 1c 4 (80 .+-. 3% RCC) (0% RCC) 3
##STR00089## ##STR00090## 1s 5 (70 .+-. 7% RCC) (0% RCC) .sup.a1 h
pre-incubation time; 2.3 .mu.mol of precursor; 140 .mu.mol of
TiO.sub.2; 130.degree. C., 5 min; 40 .mu.l total reaction volume;
no magnetic stirring; radioactivity introduced as 10 .mu.l solution
of aqueous [.sup.18F]fluoride (1.5-4 mCi) containing 0.36 .mu.mol
TBAB. ~80% of radioactivity extraction efficiency (REE) observed
for every entry.
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EMBODIMENTS
Embodiment 1
[0302] A method of forming an [.sup.18F]-labeled organic compound
in an aqueous medium, the method comprising:
[0303] combining within an aqueous medium an aqueous [.sup.18F]
fluoride, a transition metal oxide and an organic compound
precursor comprising a reactive carbon; and
[0304] allowing said aqueous [.sup.18F] fluoride source to react
with said reactive carbon thereby forming said [.sup.18F]-labeled
organic compound.
Embodiment 2
[0305] The method of claim 1, wherein said organic compound
precursor is an aryl organic compound precursor and said
[.sup.18F]-labeled organic compound is an [.sup.18F]-labeled aryl
organic compound.
Embodiment 3
[0306] The method of one of claims 1 or 2, wherein said aqueous
medium is less than about 5%, 10%, 15%, 20% or 25% water.
Embodiment 4
[0307] The method of one of claims 1 to 3, wherein said
[.sup.18F]-labeled organic compound is a positron emission
tomography probe.
Embodiment 5
[0308] The method of one of claims 1 to 4, wherein said reacting is
SN2 nucleophilic substitution reaction.
Embodiment 6
[0309] The method of one of claims 1 to 5, wherein the reactive
carbon forms part of a substituted or unsubstituted aryl,
substituted or unsubstituted heteroaryl, substituted or
unsubstituted alkyl, substituted or unsubstituted heteroalkyl,
substituted or unsubstituted cycloalkyl or substituted or
unsubstituted heterocycloalkyl.
Embodiment 7
[0310] The method of one of claims 1 to 5, wherein the reactive
carbon forms part of a substituted or unsubstituted alkyl,
substituted or unsubstituted heteroalkyl, substituted or
unsubstituted cycloalkyl or substituted or unsubstituted
heterocycloalkyl.
Embodiment 8
[0311] The method of one of claims 1 to 7, wherein said transition
metal oxide is chromium(VI) oxide, molybdenum(VI) oxide,
platinum(IV) oxide, rhenium(VI) oxide, rhenium(VII) oxide,
ruthenium(IV) oxide, tantalum(V) oxide, tin(IV) oxide, vanadium(IV)
oxide, vanadium(V) oxide, yttrium(III) oxide, zirconium(IV) oxide,
chromium(III) oxide, bismuth(III) oxide, manganese(IV) oxide,
tungsten(IV) oxide, molybdenum(IV) oxide, tungsten(VI) oxide,
palladium(II) oxide, iron(II) oxide, zinc(II) oxide, indium(III)
oxide, copper(II) oxide, niobium(IV) oxide, niobium(V) oxide, or
titanium(IV) oxide.
Embodiment 9
[0312] The method of one of claims 1 to 7, wherein said transition
metal oxide is palladium(II) oxide, iron(II) oxide, zinc(II) oxide,
indium(III) oxide, copper(II) oxide, niobium(IV) oxide, niobium(V)
oxide, or titanium(IV) oxide.
Embodiment 10
[0313] The method of one of claims 1 to 7, wherein said transition
metal oxide is TiO.sub.2, NbO.sub.2, Nb.sub.2O.sub.5,
In.sub.2O.sub.3, or CuO.
Embodiment 11
[0314] The method of one of claims 1 to 10, wherein said aqueous
medium further comprises a base.
Embodiment 12
[0315] The method of one of claims 1 to 10, wherein said aqueous
medium further comprises an ammonium base.
Embodiment 13
[0316] The method of one of claims 1 to 10, wherein said aqueous
medium further comprises an ammonium bicarbonate base.
Embodiment 14
[0317] The method of one of claims 1 to 13, wherein said aqueous
medium further comprises an alcohol co-solvent, optionally MeOH,
EtOH, n-PrOH, i-PrOH, t-BuOH, tHexOH, n-octanol or
cyclohexanol.
Embodiment 15
[0318] The method of one of claims 1 to 13, wherein said aqueous
medium further comprises an alcohol co-solvent, optionally t-BuOH,
tHexOH, n-octanol or cyclohexanol.
Embodiment 16
[0319] The method of one of claims 1 to 15, wherein said reactive
compound or said organic compound precursor is attached to a
tosylate moiety.
Embodiment 17
[0320] The method of one of claims 1 to 16, wherein said aqueous
[.sup.18F] fluoride is generated from a cyclotron and is not dried
or azeotroped after generation from said cyclotron.
* * * * *